All that matters is that the paperwork is correct with the title company.

That would be $3000/year, and I guess that would mean my annual return would be 8.9% at this point (3000/33400 = .089 = 8.9%).While that 8.9% sounds all fine and whatnot, and suggests that using the HELOC in this way is eventually a better return than paying the entire 50,000 in cash, I'm really struggling to grasp whether this is a correct way of thinking about things.After all, if I were to pay 50,000 in cash now, I would start getting the 6% return right away.

I think you choose correctly going into this investment segment.Regarding servicers - I have tried few, and the best in my opinion is Madison.If you would like me to share my direct contact with you please send me PM and I will be happy to assist.Eran

If I understand correctly, the tenant has not yet moved out, has properly noticed lease termination at the end of April, and has not paid April's rent.

Oceans of red tape must be navigated, but if done correctly, very much worth the journey. 

Verify the rents are correct and the tenants are current on all their payments.Why are you moving one of the tenants out? 

Your path forward is dependent on what you value most, there is no single correct path.This might not be popular opinion but I prefer to pay only a little more than the minimums on debts and then save/invest as much as possible into a variety of things, rather than paying down debts and having nothing left. 

What if we have a market correction?

That is correct, if you are using the money for personal expenses.

Although what everyone above said is correct it will not always be the case.