Good on you for taking on this task! It does look like you are off to a nice start. I'm not completely clear on what you are asking. A plant that needs certain conditions to grow well will always need those conditions, but some plants have a broader range of what can make them happy. Any garden will need some care. Mulch will break down and need replenishing, but depending on the type, once a year or even every other year is enough. You can keep weeds down by mulching everything with mulch that is slower in breaking down. For instance, if you use pine needles (often easy to find here in NH piled on the curb at this time of year) on your beds and chipped wood (befriend your local tree service) on the paths, everything will be mulched inexpensively or for free with weed-seed-free mulch, but your planting and walking areas will look different. I have areas that I weed only once or twice a year due to lots of mulch and what has by now become rather dense planting. Your perennials will look best if dead headed at least after frost in the fall and old foliage is clipped down in the spring before new growth starts. (I'm assuming that our NH snow will cover old foliage much of the winter, and leaving foliage seems to reduce spring frost heaving here in central NH.) As Tiffy noted, tulips won't perennialize well (adapt) but daffodils will. Put in a few with bulb fertilizer the first year, and after that they will pretty much take care of themselves in my experience, increasing slowly in areas with less optimal conditions, and increasing quickly in areas with great conditions. You can do trial by fire with the perennials - some things will like your conditions and do fine, while others may not. Having started with plants that are tolerant of less than ideal garden conditions, you've bettered your chances that they will do well. The ones that don't can be replaced by those that seem to like the conditions you offer. One thing I've learned from unfortunate experience with public plantings near the road - don't plant anything unusual or precious to you as things may disappear . . .

Very dependent on local labor, and for a sewer line the depth of the line below grade. Shallow lines around Northern, VA often run about $200 a foot, with deep lines or lines under concrete or asphalt ending up closer to $300.

It depends :-)) And isn't that the answer to any gardening question? LOL! Some short-lived perennial will take well to division while others not so much. For example, the perennial wallfllowers like Bowle's Mauve, which literally blooms itself to an early demise, are more shrub-like and typically have a single growth point which limits the ability to divide. And dividing delphiniums is just a guarantee of killing them, IME. Never had any success dividing lupines either, but they will reseed easily and replace themselves. One of the best resources for care of a huge assortment of perennials as well as how, when and if to divide is The Well-Tended Perennial Garden, by Tracy diSabato-Aust. This is a great reference any perennial gardener should have in their library.

One waterproofs from the outside, not the inside on a new home. If there is a concern about a great amount of water, the builder can add further barriers to the outside and under the slab, as per the Delta illustration below. (The footing barrier, which stops rising damp, has been part of the Ontario Building Code for more than 10 years already.) As for finishing the basement walls, any space between insulation and the wall will short-circuit the effectiveness of the insulation. Unless there is an interior footing drain to collect any water behind the interior membrane, all the plastic will do is trap moisture for mould growth between the plastic and the foundation wall. It looks like the builder intends to pour over the plastic that extends onto the bottom of the excavation. I don't see the logic behind this arrangement.