Hello Jacob,The most important decision you will make is the location, not the property.

We are old enough to do that without penalties, but that may have some unwanted tax implications due to our current W-2 income.What's going to be the best way to analyze our options and make a decision, and if it IS to get a HELOC, are there any recommendations?

Do all decisions need to be finalized before construction begins?

Since they are reliable in terms of their rent, you may want to let them the know the reason for your decision and give them the option that you might be willing to extend the lease based on the new terms which would include the deposit, pet, etc.

We want to make the best decision, because we're likely to stay for a long time with the company we choose since it's a lot of work to switch. 

Tough decision but at the end of the day you're selling an asset to buy another asset.

I told her I'd have to discuss it (I don't really, it's my decision) because that is twice the size we typically allow.

Every decision you make with regards to every deal you make should be made based on the next move you are going to make, which is dictated by the REI Plan you've already designed.Your next move is to design that plan.

Besides legalities, is cost and ROI the driving factor in the majority, if not all of your repair and upgrade decisions?

Every decision you make should will be based on that specific "next thing" you will be doing.