First of all, when you said "I don't plan on being at this house too long", what kind of time frame are you thinking of? A year? A few years? A decade? If it's for less than a year, I personally would be working on engines, rolling stock, and buildings. I'm actually in such a "between" situation, and I'm working on engines (in addition to working on my brother's HO layout).
For a space like that, assuming that I would get generous space in the future, and assuming that I'd be in each location for at least several years at a time, I would build it removable modules/sections. I'm not talking about something like an N-trak module, as those standards are rather limiting (unless you wanted to so something like that, of course). I'm talking about choosing several "scenes" (whether prototypical, or based on a prototypical scene, or completely imagineered), like an industrial area, a yard area, an engine area, a bridge scene, a "loop" scene, whatever. Instead of restricting myself to certain cookie cutter sizes that would fit in a certain SUV or mini-van, I would only restrict myself to a size that could be moved out of the basement, into a moving or rental van (or even a PODS container for storage). It's okay if certain scenes like a long yard has to be designed to be in two or more sections, simply design them that way.
The idea (not a new one, I'm just going off of other's already published ideas) is that you only take these certain, special "primary" sections with you when you move, and arrange them as space allows in the new location. When you set the "primary" sections up, you "connect" them with "secondary" sections, which are mostly left behind (basically tossed) when you leave the current location. So, you put most of your effort into the primary sections that will be taken with you wherever.
You design the sections so that they are "semi-permanently" attached. The frame work, subroadbed, scenery base (as in foam that is shaped for mountains), and the like is designed so that they can be unscrewed and removed without cutting. Things like trees, bushes, track, ballast, roads, etc. are installed as normal, as if everything is part of one permanent layout. That way, everything is visually seamless, and cutting scenery and track at the joints will take little effort, and the sections become removable with little damage to the layout sections (and connection in the new location won't be too difficult).
Also, since you are comfortable with multideck arrangements, I would design the primary sections so that they just sit on the framework (and held in place with either bolts or screws or the like). Again, that way you can build the framework itself to match the location, and at the correct elevation. And you can re-arrange some primary sections as needed in the new location, without having to raise/lower or add/remove table legs/wall mounts. That will also put less stress on the sections as they are removed and installed.
And when you are just starting out, you can simply connect primary sections with dull, unscenicked straight track from one to the other, then as you get to the secondary sections, you can redo the track in a more planned manner. That way, at least some trains can be running in the meantime.
Regardless of whether you are doing a sectional or a permanent type layout, starting with desired scenes and locations is always a good place to start. Then arrange those scenes and add/remove as priority allows. You could either do this on the computer, or if you are more comfortable, cut out pieces of paper to size, and fit them around something like your graph paper plan. And remember, just because you have the space doesn't mean that you have to fill every inch.
But yeah, I would do a sectional approach, where everything is still visually seamless, but you won't destroy the layout when removing it for a move (like so many people have found fatal to the layout, like Bruce Chubb found out when he tried to simply save sections of his permanent home layout).
---jps