We went over budget due to unforeseen structural issues that came out of our own pocket.

Are you ready for unforeseen issues? 

I work for a commercial GC and we always do contracts which you should do and also I would, although it may be a little more expensive, have a GMP in the contract so you know what your max price will be barring any unforeseen conditions.Let me know if you have any questions!

Unforeseen things and expenses will pop up. 

Initially I like to have at least $10k in reserve after I purchase for any unforeseen circumstances.

Does it last, hide defects in structure unforeseen even from inspection, etc. 

If you have 20 rentals cash flowing $100 each, make $200,000 a year, and have a $250,000 line of credit, then you probably don't need any reserve.Life brings unforeseen expenses.

However, in reality, it could be more, due to vacancies and unforeseen issues.

I do realize that no matter what there will be  unforeseen expenses, and I like to consider myself handy enough to tackle most repair tasks. 

How best to decide on major CapEx expenses (ie, vinyl windows that may last 20 years but are cheap vs aluminum that may last 50 but are expensive)How best to handle what happens if/when one of us wants out of this in the future for some unforeseen reason?