You can operate in as many states as you want, but you can not use general solicitation and advertising, and must have a preexisting relationship with any investors to whom you offer the investments.

What is the best way to find out if I will not get into trouble with some preexisting liens?

I have sold properties that were winterized as part of the standard protocol, but that had issues that were probably preexisting. 

The problem with using a pre-existing LLC is that you are often adding whatever liability which rests in the existing LLC to your new property, so it can be a good idea to start fresh.

Lease generally has tenant has to bring property back to pre-existing condition if they decide to leave including remediation clean up.

Of course with HOA foreclosures the buyer is still responsible for the pre-existing mortgage, so always pull title before purchasing.

That's even if you didn't build the wall and it's pre-existing.  

If it is 506(b), you can only offer it to people with whom you have preexisting relationships.

It wasn't a brand new house and you hadn't touched the underground plumbing so it was a preexisting condition.

With that said I did join a program to educate myself so that I can qualify as a sophisticated investor and meet people and establish a pre existing relationship.