HVAC contractor sees the age of the unit and jumps right to "you need new" approach.  

I wanted some advice on that and maybe a different approach I could take for my first property without putting much of my own money in. 

A neighbor approached me and asked to rent one spot.

If yes, and you haven't been enforcing it, I recommend taking the good ol' Brandon Turner approach. 

I have been approached with buying a condo in an up and coming area close to Dallas, TX.

That is fairly healthy in my experience, but this also looks like a large home.  

It's a really good way for me to burn calories and keep lean (I typically don't eat anything while working on a property - maybe a small snack during the day - and so that helps also with being healthy). 

Granted, as I approach the $1M budget, I'll be most likely looking at a commercial situation (5+ doors), at which point my personal income may not matter.

While this might work out for you, I would consider it the more extreme and risky approach. 

If you chose to reinvest that money you should be able to make it make much more than $800/month.An alternative approach if you strongly believe that future value will be much higher would be to harvest the equity and keep the property, but the new mortgage would essentially destroy your cash flow.