Re: Floor leveling
Self-levelling floor compound is gawd-awful expensive. If you have a large area to do, then use a sand-mix to build-up the area, then apply self-levelling to get a smooth/level surface. It is heavy - but not so heavy that it would structurally harm your house UNLESS your house had a pre-existing structural problem.
From your description, you house is like mine. I have a 2" dip over 4' due to really bad construction. I used Ditra to strengthen the floor for tiles, and didn't bother levelling. That wall will be all cabinets, so I'll compensate then. I wouldn't have used self-levelling as it wouldn't have really solved the problem.
The real solution is to get underneath, jack up the beam or joists, provide proper support, brace all your joists/beams/posts that are allowing the sag - and even add footings if needed. Its a labour intensive solution - but not all that expensive - and then you don't have to worry about further sagging/cracking, etc.
"Time is a great teacher, but unfortunately it kills all its pupils."