I do discount useful life and increase costs to be on safe side. 

I would try to get him to take possession earlier for a discount so at least you have utilities and etc out of your name and some money coming in earlier even if he doesn't fully move in earlier.

The bathroom is right next to the kitchen.

Try looking into zillow/Redfin and see what your potential rents you can get near the neighborhood by filtering the bedrooms/bathrooms of the intentional property that you are planning to buy.

Can the deal be discounted if the GPs were investing their own $ too?

Elite Tier pricing, usually reserved for The Home Depot customers after spending $100k in a year, unlocks meaningful discounts on renovation and maintenance materials.Save Up to 20% on Paints, Stains, and Liquids: Save up to 20% on paints, stains, and other liquid products from The Home Depot's extensive selection.

After about 1.5 years of owning them, i did some minor cabinet upgrades, bathroom upgrades.Zillow and all other real estate websites show the current value at $120-125 K.

Purchase price: $490,000 Cash invested: $61,000 Sale price: $649,000 Nestled in the highly sought Silver Sands neighborhood of New Smyrna Beach, this 4-bedroom, 2-bathroom home offers the ultimate coastal living experience.

in my experience this will solve the issue, especially if you don't want to sell at a discounted price

Gut rehab, all new kitchens, bathrooms, all new EVERYTHING.