Then fill the rest of the way with clear gravel, not dirt along the perimeter a plastic drain membrane should be placed on top of the footer to at least an inch above the surface of the new cement floor.

It is a membrane that you can lay over concrete or plywood and then you can thinset over that.

Then, again depending on what type etc etc, install insulation boards (usually ISO), Membrane (NOT just 30lb felt!)

The roof is still tar and gravel according to the tax card, so unless that's been replaced very recently, expect to put on a rubber membrane roof (once again, four stories up) in the next five years. 

If you can do basic tilework: put in a proper CBU substrate, apply a membrane of some kind and set tile in thinset, It doesn't matter that much what tile you install.

The plan though is to sell the house in two years and I wouldn't want to sell anyone something that wasn't built right,You would want to lay the concrete / cement below the leveler in all of the cracks (don't count on the leveler to fill them), then use schluter ditra below the flooring if you're going to use tile.Ditra is expensive but worth it - https://www.homedepot.com/p/Schluter-Ditra-54-sq-ft-3-ft-3-in-x-16-ft-5-in-x-1-8-in-Thick-Uncoupling-Membrane-DITRA5M/100143471Otherwise, based on the info given, I would focus on drainage and monitor the situation.  

If it's a flat roof, there may be a chance that the insulation is on the top of the roof deck if you have a membrane or built up roofing systems.  

As Sergey said above, "Ice and Water" membrane are very important, especially in a place as wet as AL. 

If you make prudent use of acoustic sealant and/or hang a second layer of 1/2" drywall over the fire rated - with a liquid acoustic membrane (i.e.

Your best return money-wise is to jazz up the existing layouts as much as possible.While the floors have held up impressively, I'd still get down there, tap out the mosaic tile piece by piece, skimcoat with thinset, RedGard, and then tile over the membrane with thinset again.