These are good questions, but keep in mind that a month of obsessive research is still the absolute tip of the iceberg. Here are my best answers:
1. I would focus on a duplex first so you learn house hacking and management of one tenant. If you are single, look for uneven multis where you can live in a small unit and rent out the bigger one (e.g. - 1/1 and a 3/2 instead of 2/1 and 2/1)
2. Yes, the more units you go up, generally the less players in the game so there is some advantage in purchase competition as you go up, but also more management scale and cap ex for someone who is new.
3. Do not focus on the best price for properties when you are new. That will get you looking at cash flow and end up in a lower rated area than you think. You want the price that works for you in the best appreciation potential area possible. Your relationship with an investor-friendly realtor will be crucial here.
4. If you are house hacking, you wouldn't use a HELOC, you would just refinance. You could use a HELOC, but with VA loans you have an allotment so you can get loans on more than one home depending on how much bandwidth they give you.