The 'moisture' that is being absorbed naturally by such a cheap porous slab (that obviously lacks any form of insulation & vapor barrier when poured) is going to wick through the slab.

That means a proper business entity structure to insulate you from as much liability as possible in the event of a lawsuit.

Most properties in Nebraska are built for the seasonal conditions we go through meaning we typically all have heating, A/C, good insulation, basements (for severe weather), etc. 

From then on, you're largely insulated from exchange rate drama (since you'll be servicing the debt, collecting rents, and paying expenses, all in US dollars), at least until you sell.Also, while in theory you probably could structure an owner financing deal with a variable rate tied to the US/Canada exchange rate, you're probably better off keeping it simple and easy for a non-pro seller to understand.Speaking of which, how does that work with conventional lenders to foreign nationals?

Houses that old were built with little insulation; some has probably been added during the years, but you might want more to keep the heating bill down. 

I don't see any insulation either... is that part of the rehab budget?

I've done multiple tear offs and you're budget (assuming a standard building on a standard 25x125) is in the $8000 to $12000 range depending upon the extent of plywood replacement and R value on the insulation you put in.

The inside was slightly discolored, obviously if water is going to go through shingles, then run down wood, through insulation and into sheetrock it will not be crystal clear anymore.

However, if the numbers are on the tighter side then forcing the repair might be a good option to use and still close the deal.I would assume that if you were able to get responses from a number of others on the site they would probably say things like I am going to list here.1) Problems can seem small and simple at first but grow larger in a hurry - it happens.2) Depending on the type of shower/tub installed in the above unit it may be more than a simple fix and get into much more money than you think - you won't know until you open the ceiling for sure.3) After the plumbing repair you could be looking at mold potentially in the joist spacing area between units.4) Depending on the length of time the issue has existed and been patched to get by you may also have damage to the wood - joists between units and or sub floor issues under the upper unit tub/shower.5) If there is insulation between the two units, you may have soaked and degraded insulation that needs to be replaced as well - good news is that rock and insul are cheap to replace.6) OR......... you may have someone open it up to fix it and its just a simple plumbing issue and is a quick and easy fix - totally possible too.Just as an illustration, I went to replace a bath faucet for an accountant friend of mine yesterday.

I work for a window company, and although I am in Canada, some info could be relevant:the most insulation you get from the most to the least: fixed, awning, casement, sliders, hungthe most expensive are usually awning and casements, then hung and sliders, and then fixedif choosing between vinyl and wood, I would recommend vinyl.