Sounds absolutely fine to me! 1)-3) No comment 4) The insulation will make little difference as far as sound proofing. If keeping the noise down is a big priority, use a damping system such as Quiet Rock, Green Glue or resilient channel and an extra layer of drywall. 5) If the heat pump doesn't keep humidity below 35% RH, you can always put in a portable dehumidifier. 6) If the inspector is uninformed and therefore insists on a polyvinyl vapour barrier, it won't hurt the system. There's no need to bother with Membrain, which is designed to be effective with fibrous insulation. On one project I did with cc on the walls, the inspector approved it without poly. On walls with XPS, inspectors have insisted on the poly.

The intended purpose for laying down plastic is to retard the transmission of soil vapor (which is in almost all soils except in extremely arid areas, and inexorably rising due to changes in barometric pressure) from coming up into the basement space. The fact that you are using a dehu means that you have a perceptible soil vapor problem (at least that's why you are paying the electric co. to run the dehus, which is comparable to running an A/C, in some cases). Note however, that I said retard, not completely prevent the rising of soil vapor into the basement atmosphere. Nothing I know of will completely keep it out. Because we now have a goal of sealing up our houses in the name of energy savings (and have modern, and different, whole-house heating systems) rising soil vapor can get stuck within the building potentially causing damage to the structure or contents or residents, if mold develops. Of course your house, like mine, was built with long-tested systems that did not expect, or require, the house to be as hermetically sealed as we sometimes try for these days. In 1857 the vapor was a-rising just as it is today, but it was exiting the building much more easily. Two other factors: people lived and worked at home and were more likely to be aware of and able to adjust the basement openings during the day, promoting additional passive ventilation to remove the moisture. And they may have highly prized that very same moisture if they stored food in the basement. Of course they also didn't have nifty stuff like cross-linked plastic molecules made into cheap (if you don't take into account any off-stream environmental costs), easily laid-out rolls of plastic to put to use, either. Soil vapor is also coming from the basement's walls as your inspector noted. But blocking that moisture is as hard as, or harder, than blocking the soil vapor. If you had thoughts of converting your basement to modern uses (family room, media room, exercise parlor, etc.) you may be disappointed as this is rarely successful in old houses such as ours. So the remaining issue seems to be: how tight is the house above the basement, and how might that tightness be interfering with the house's natural ventilatory patterns. (I think of it as how the house is "breathing", albeit in a passive way.) And of course, it also depends how much more you may be planning to do, in the name of energy conservation, to further tighten up the house. You have run smack into one of the central dilemmas of old-house care: how do you integrate (without doing damage) modern building and energy standards with a structure that was designed and built to support a completely different system? Solving one problem can easily create a new, perhaps more difficult to manage, unforseen issue. There are many opinions and oxen-to-be-gored in this arena. As a practical matter, if you want to lay down plastic (though I recommend special-purpose materials intended for vapor retardation instead of construction poly) and can seal it well with tape where sheets are overlapped, and along the bottom of the walls, you can susbstantially reduce the amount of rising vapor within the basement cavity. But you should know there are some who posit that doing so will shift this moisture (perhaps with damaging consequences) to adjacent soil spaces, including under and in the immediate, exterior vicinity of your foundation walls. This (according to some) may super-saturate the soil, disturbing the necessary firmness and creating settling or susidence problems. Does it? I surely don't know, but it does create - over time - a very moist soil under the plastic. (You can test this by laying a yard-square scrap of plastic on the dirt floor and see what happens.) Others recommend various systems of forced, or air-pressure augmented passive ventilation to remove the moisture laden air from the basement before it can rise into house interior and replace it with (theoretically) drier exterior air. This method has the advantage of not monkeying around with existing soil mositure states, but it is complicated, and may take personal attention to adjust during each day and/or electricity to run. If you have just purchased this house, I think you should observe the ebb and flow for a while (at least a calendar year), as you think about this. And keep the issue in mind as you contemplate any further sealing and insulation projects. It sounds as though the dehus are keeping things in check, so nothing (except cost of power and fuss of removing condensate) is lost by taking a go-slow approach. And by all means, test for radon if you have it in your area. (Your local or state health department is a resource on this.) An upside of the necessary ventilation to control radon can be a reduction of basement moisture since the gas and at least some of the air vapor are removed at the same time.

Is it normal for a 50+ year old house basement to fail? Yes. Eventually all basements start to fail. It may take years and years, but water/moisture will find its way in. It just depends if you want to fix the problem. It could be as cheap as fixing a sloping sidewalk or as expensive as a whole basement wall being dug up and re-water proofed. Unless you want to finish the basement you really don't have to do anything. Unless the ground is pushing in the foundation wall. Just keep on cleaning it up. Of course it will effect the re-sale.

@Ryan Thanks for the question. A concrete slab that is sitting ON the earth (ie. not in a high rise on the 10th floor) always requires a vapour barrier underneath. Always. If anything, it maintains your warranty. There are three definitions of slab concrete: 1. Below grade. This is normally poured concrete for a foundation that has been dug into the ground. Like a basement. Even if 1 square inch is 'below grade' we view it as ALL below grade. 2. At grade. This is a common situation. Concrete is poured onto the ground and the house is built from there...going up; not down. Again, this is sitting 'on the ground' therefore it is considered 'damp' until proven otherwise. Even in the desert areas, we find dampness in slabs that are sitting on the ground. Moisture LOVES to condense on cold surfaces...like concrete. 3. Above grade or 'suspended slab'. This is the 'high rise' situation. You don't have to be in a high rise. It just means the slab is suspended in the air. It touches nothing but air above it and below it. This is the ONE situation where you can 'get away' without a vapour barrier. But you still void the warranty as soon as the contractor starts laying the first run. The installer is responsible for installing product on-site. If you did not purchase the vapour barrier, then the installer did not install it. If you used the SHOP'S installer, then they are responsible for ensuring you purchase everything you need for the job. Which requires you to tell them what your situation is. You get what you pay for. A good flooring installer *should have pointed out you needed a vapour barrier. And then would have told you what to purchase for him/her, or they would have said, "I have some in my truck, it will cost another $1/sf for the materials plus $0.50/sf to lay it." Something like that. And the preparation of the concrete is another thing that should have been paid for and performed. But so many contractors just want a paying job, that they offer the 'no frills' install. They get there, they install what is needed/purchased/sitting out for them and then they go home with a pay cheque in hand. I've had experiences where my QUESTIONS to the homeowner caused them to hang up on me. Yep. The question, "Is this for a bathroom?" caused such angst they started to yell it was none of my d@mn business and hung up on me. OKee DOKee then. I don't know what your situation is. The above is just an example as to why a store, with highly trained FLOORING professionals (ahem...a flooring store and not a 'big box' store like HD) would miss something as simple as a vapour barrier for a concrete slab.