Questions about HELOC, Banks, and Rent by the Room

[Joseph Nguyen]

Hello! I wasn't sure where to post this, so hopefully this is fine. 

I'm a new investor in Dallas, TX! Hoping to connect and learn from others! I recently purchased a SFH (4 bed/ 3 bath) in Plano via First Home Buyer/owner occupied conventional loan and am renting by the room. I currently rent out 3 of the 4 rooms (all MTRs) and keep 1 for myself. However, I'm also a travel professional and am usually away from my home months at a time for each contract that I do. I originally thought I had to occupy one of the rooms (it being owner-occupied), but I've heard people say that they were in the same situation and would just sleep on the couch. My question is:

For the time that I am away, would I be able to rent out the 4th room as a MTR as well? 

As for HELOCs, how does one use one? I know it's a line of credit, but would I receive a card / account number? Wondering how I would access it.

Also, looking at opening a HYSA with Sofi or Ally for when I get more properties. I was seeing if anybody had experience using either one? Wanted something for easy transactions for rent collection, bookkeeping, etc. 

Thanks in advance for any advice!