The first roofing contractor proposed spraying over the existing roof with polyurethane foam.  

Welcome Keela..my answer is simple..if you do what you say you're gonna do people will respect that...i started young, and still look like i'm 16 when i shave btw..some people looked at me funny at first, and some still do..but when someone needs to sell a property, and you're there to buy it and close, they'll respect it and come to you again, regardless of age..similary, if they see you building a reputable portfolio of rentals, or a successful flipping business, they'll repsect that as well..i do honestly think it's a bit tougher for a younger person to earn that respect, but you can make it a lot easier on yourself by following through with every little thing....return phone calls, christmas cards to attorneys, lenders, etc. thank you cards..whatever it is...good luck :)

They are in their 20's, have some 31 units paying them rents and have never held jobs.

Sign P&S have your attorney review, make sure you are able to assign the contract.

I would most definitely spray foam the basement walls. 

Broker participants and their agents must input exclusive right to sell or exclusive agency listings on one to four unit residential property and vacant residential lots located within the service area of the MLS within 72 hours (with no exceptions for weekends, holidays and postal holidays) after all necessary signatures of seller(s) have been obtained on the listing (7.5) or they will be fined.

Get memory foam beds.

I've replaced a few roofs, two with metal, one with tpo, and another with tpo but we had to add a bunch of foam to get a positive slope on a flat roof - i could not believe how much ponding i had but that's another story. 

You can then have he/she run the calcs and plug in an upgraded type of insulation to say spray foam for example.

My thought with purchasing before the deployment is that I would have about 6 months to renovate prior to leaving, and It will shave about 10 months total off of the year requirement to live in the home before I come back that is required with the FHA loan.