We have a similar issue with our fireplace and, after considering various options, reluctantly decided not to disturb the overall structure. I would caution against removing the hearth. It's there for a reason: It's noncombustible and that's important protection against a fire. Lowering the firebox to floor level and then installing a hearth at floor level will probably be a very big, very messy and very costly undertaking, almost like rebuilding the whole thing. You might be able to remove the raised hearth and install a floor level hearth in its place. I think that would be okay from the safety standpoint, provided the new hearth is about the same size at the old one. You will then need to extend the fireplace surround so it goes under the firebox as well as over and on the sides. That sounds like the work of a mason, or maybe you can install metal -- either copper or powder-coated steel in black so it looks like cast iron, if you like that look and think it will blend. If you want to reduce the size of the firebox, you could consider a fireplace insert. The most popular ones are gas-fired, either natural or propane. They are expensive ($3-4.5K), and typically come with fireplace surround to cover the old firebox opening. I would guess that the kinds of changes you are contemplating would total about $6K or more. And picking a competent installer involves a leap of faith. Ask a fireplace contractor for a free estimate. Then you'll know.

Propane tanks are only filled to 70% max. Daily household usage is minimal (vs using propane for the type of backup generator we have that uses a gallon per hour). You pay more for the gas due to low usage but it should not be prohibitive. Alternately, induction cooktops that are highly regarded include Miele, Wolf and Bosch. Thermador has a very beautiful one. I was researching them for a possible retrofit. The downside of induction, depending on the cooktop, is losing space below -- I have a high usage utensil drawer there. Also induction-friendly cookware is required. But those who have them seem to love them. My girlfriend got an Electrolux induction range and loves it. You might take a look at that. The induction site has the most technical info in one place. Here is a link that might be useful: The Induction Site

What exists currently is a fire hazard and needs to be changed regardless of anything else that you do. You cannot have wood directly above a cooking zone unless it's at least 30" above it. Overhead venting is always superior to downdraft. Especially if you want to convert to gas. A strong wind right at a gas flame tends to do funny things to it. Like suck it out. Overhead venting captures naturally rising steam, grease, smoke, and odors, and if you can have the correct ductwork added, gets all of those nasty things outside of your home. Because all of that stuff rises upwards and outwards, vent hoods always work better if they are at least 6" larger than the cooktop that they are covering below, If you move to a 36" cooktop, you would ideally have a 42" vent above it. And at least 27" deep. For your wall oven, if you want to replace it, your cabinet needs to be the right size to accept a modern oven size. That standard has become 30" ovens, which usually take at least a 31" cabinet in custom cabinets, and a 33" cabinet in standard dimensioned cabinets. It looks like a 24" oven in maybe a 25" cabinet? You also need to check the spot where the fridge is, and measure it. It too may not be a standard size to work with today's appliance sizes. A regular free standing refrigerator needs 36" of width and 70"-72" of height. I'm also not seeing any drawer stacks in the picture that you posted. Many older cabinets didn't see the usefulness of drawers, so all you got was a single one on top of doors rather than a whole stack of drawers. Are there any roll outs below, or is there just a half shelf? Site built continuous cabinets with no internal divisions? If everything works currently, other than taking down that shelf immediately above the cooktop, I think I would just live with it for as long as it took to accumulate the funding to address the rest of the 30 year old issues that the kitchen has, not just the appliances. One other approach that you may not have considered if you decide to keep the cabinets and just retrofit them is a 48" actual range where the cooktop is, with an actual hood above. That will give you two ovens. Where the oven is located now could be retrofitted by a good cabinet maker to accept a MW on a shelf so that one could get off of the counter. Maybe you could do something like a cutting board/baking sheet rack similar to a plate rack with the leftover space from the oven cabinet.

While you are waiting for further responses, you might try searching on "OTR" and the 240v Advantium. There have been numbers of recent discussions of both subjects and those threads may shed some light on the subject of how well they work as second ovens and microwave substitutes. Also, you might find some useful info in the current thread on "speedovens vs. microwaves?" I don't recall a recent thread that is specifically about using the 240v Advantium OTR above an induction range, but Advantiums have been in use for the better part of a decade and there may be some discussion of the topic of how well they work as a second oven. As for venting performance. the knock on OTR units generally is that you've got a flat bottom surface that only extends over the back burners and the vent/intakes depend on suction to draw vapor from pots on the front burners. It is just less effective than a larger dedicated range hood, particularly a canopy hood. My recollection is that LG made an OTR with a slide-out vent-pick-up tray that extends over the front burners but I don't think it had a full-on oven capabilities like the Advantiums. Anyway, we deal with the kitchen spaces we have and OTRs are sometimes the option that fits. The fact that a canopy hood would be better may not matter in such situations. IIRC, Luv2putt posted on using an OTR with his Viking induction range and was reasonably happy with it. I think there have been some discussions of folks who were satisfied in using OTRs with Wolf and NXR all gas ranges, as well, where the venting needs are more strenuous than with induction. If you want to search for those posts, Nunyabiz1 is a name that I recall having posted on the subject. On looking at a Samsung first, be aware that there are three different Samsung induction ranges currently available in the US market: two freestanding models (NE597NOPBSR and NE 595NOPBSR) which have been on the market for three years and are priced between $1200 and $1800 depending on model and holiday sales pricing, and the slide-in with the divisible oven (NE58H9970WS) which was released last fall and runs $2500 to $3k plus depending on vendor and holidays. The slide-in has a lot to recommend it but there are some limitations including having only 10 burner heat settings (the freestanding models have 20). I haven't seen much info on how well the divisible oven works when the divider is in place, but Samsung has been selling Canadians a freestanding version with this feature (NE599NOPBSR) and you could look for reviews on that range.