Maybe think of your porch floor a little more like a roof ... I, too, have an old house with incorporated porches (front and back) that sit over top of a full basement foundation (brick with original stucco.) We restored the back porch as a "sunroom" (it was closed in some time in the 30's) and I noted that roofing tar paper was used between the sub floor (plank) and the original T&G porch floor. There are shreds of roofing tar paper hanging on the edges of the bottom of the front porch floor where I can find it, but the old wooden floor was replaced with plywood and then the porch floor was tiled by POs (a bad DIY with 1 inch grout lines that leak like crazy, making my repair job that much more difficult.) The pitch on both porches is good (away from the house) There are low shingled walls all around the porches so water would be trapped without some sort of system to remove it. The front porch uses a pitched trough with 2 exit tubes at the foot of the short wall but I found no evidence of this on the back porch. These 2 devices (the roof paper and the trough) surely would have worked well if they were maintained, alas, the metal trough is rotted thru and leaves/critters were getting into the basement till I discovered the holes and band-aid-patched them till I can address repair of the trough properly. (interestingly, the front porch foundation was hidden behind a finished wall in the basement and was only found when we had a termite inspection done.)

It depends on many factors. I prefer to do what we call a bonded mud screed or "dry pack" floor most of the time, other times self leveling can work but from what you've mentioned i don't think so. You have to thick of a pour for most all self levelers. and they are tempernmental in cold climates over crete. Share some pics, condition of the slab?

Currently the floor can receive sheet goods - that's it. Carpet, sheet lino or sheet vinyl. The wonkiness of the concrete prevents everything else. To correct the wonkiness, you need to have the paint removed = abatement. Which is something you don't want to do. Mind you, once the abatement has occurred, you can go ahead and have the concrete flattened/dealt with and then you can have ANY FLOOR you want. Whenever you want. For as long as you want. Until then, you can work with "sheet" materials like carpet, lino or vinyl.

You definitively have a big problem but there are solutions. Tearing it out and re pouring is the best option. If the concrete supplier was at fault then you have a descent chance of them replacing it If the contractor was at fault your chances diminish. I would strongly suggest pursuing this avenue The last option is having a professional apply a polymer modified cementitious coating (see video). This procedure does work but it requires someone with experience. Since your contractor left you with this mess I doubt that they would do a good job. Talk to the supplier they should have a list of qualified ppl that did this before. Good luck