If I were to approach a seller of a $200k home, and they had a remaining mortgage of $100k, could I get a new bank financed loan for that $100k, and have the seller finance the remaining $100k of equity to me?   

Additionally, I have $100,000 in cash in the bank, and my monthly expenses for my home and family are around $3,500.My wife earns between $100,000 and $120,000 from her W2 job, while I've recently lost my job but found a new one that pays $65,000 a year.

Just about any bank can open a joint account. 

Realistically, one checking account and an accounting system will meet all your needs and keep your business better organized than 7+ bank accounts.If you want to collect bank interest from excess cash, add a savings account.

Local banks.

When you go to a Bank or Credit Union, they can only offer you what products that bank or credit union offer.

I plan to BRRRR this property to pay off the seller and get my money out and was wondering if you anyone has any suggestions on banks that can do refinances for mobile homes.

if you have an LLC and both properties are under it, you just need 1 operating account.If both are under your personal, 1 bank account specifically for the rental is enough for operating.Security Deposits should always be a separate account altogether.

We also have a bank account at a smaller Chicago community bank, but there technology isn't as good to be honest.I think @Jonathan Greene's main point is don't step over dollars to pick up pennies. 

Any major bank has this account.