So keep that in mind when using a special lock system. 

People have mortgages, kids in college, caring for elderly parents or kids with special needs/ Many of them now have no idea what life is brining for them in the near future.

You are right, when the inspector mentioned the possibility or prior water damage is when you should of had that basement inspected by a contractor/professional and not listen to your agent.Gregg is right, the sellers were aware of some of the damage which is why they gave you a 5K credit. 

They offered to give me a credit on a future loan.

One suggestion to consider as I mainly do BRRRRs as well- find a local bank or credit union in the area you plan to buy that offers construction loans.

this is basically the business credit coaching partner that works with you over the course of 12 mos. to help you build up business credit for your company. 

If your credit ****** you need to hit up creditrepair.com or some other credit repair  company  and work on getting yp to about a 680 or more with you learning  from jerome.   

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

In order to execute on any of the strategies from #2, you will want to a work/income history and decent credit scores.

I prefer to have the least amount of banks as possible.Create a bank account that you already have a relationship with(Credit card or mortgage)The least amount of bank accounts is also ideal.