We had a sewer scope performed on the property and there were no apparent problems with the line (no roots, damage, etc.)As far as the radon test, we didn't have to perform one since we later discovered the house already had a mitigation system in place -- so obviously it tested high in the past. 

Because you're not getting the assistance of an agent you will be responsible with some of that part and paperwork requests, you can mitigate that by having a clear and open communication line with your seller.

The deposit should be used to mitigate loss as per the local laws.

GREAT sponsor makes a good one better and can mitigate to a large degree if a deal goes off the rails a little bit.

Another unit we found mold underneath the house that had to mitigated to the tune of several thousand.As we kept digging in, nearly every unit had something unforeseen come up.

How do you mitigate that?

Seller financing would mitigate the capital gains by spreading it out, but as @Dave Foster mentioned depreciation recapture would be due in the year of sale plus he'd still pay all the capital gains tax it'd just be over several years instead of all at once.A 1031 would make sense if he wants to stay in the game, even though there are several options that would make it pretty hands off for him.

However, just because interest rate risk is mitigated via floating rate securities does not mean this fund does not have its own set of risks......specifically as they pertain to the market value of its holdings based on certain ability to pay interest and principal pricing models and subsequently the NAV/share of the fund.

Nonetheless, a 4-plex has the perk that all the units are in one location, there's some scale, one roof, and risk mitigation because it could leave you cashflow positive even if all the units are not occupied (this would depend on the deal you're getting into). 

This option will help you to somewhat mitigate the risks of being completely inexperienced in a field of your choice.