We also have a real estate practice and it is common practice to not give the seller a lot of time before the offer expires.

After all you could just sell it after their contract expires, or pay off the remaining rent commissions and they get 0%.

Here, what is referred to legally as an "abandoned vehicle", is any vehicle with expired registration or safety check.

Is it going to take a month between tenants every time a contract expires. 

That's where I would start.That 2nd likely matures in 2035 and won't expire for a period of years after that and if that's the case it's a lien that needs to be paid and released in connection with a sale or refinance.

If you decide to keep them long I would suggest creating a USPS account and just autodebiting your PO Box dues so they dont expire.

This includes non payment, holdover from an expired lease or a 30 day notice as well as other reasons.  

I have been under contract on a property for a while now (closing was pushed back in order to allow one unit's lease to expire so as to allow me to owner occupy), and I have been in negotiations with a local lender. 

I have a “tenant” who is in my unit even though the lease expired last month.

Interview the agent; how long in business, how many and what types of properties have they listed or sold, do they understand any creative financing techniques.When you are ready (after having looked at 50 houses),  talk to the agent you like and let them know you would like for them to represent you and that you want to look at expired listings and FSBO's.