You don't NEED either right off the bat. Don't get caught up in the weeds.
Just get an RODI system that seems good to you. Hook it up per the instructions to a COLD water supply. There are lots of ways to do this, it will depend on your situation. (It is the easiest thing to place it where you make water for the tank, I think. A laundry hook up is easy to hook up to if you have that sort of thing,)
You can always add a booster pump later on IF your water production is too slow. I have the RO Buddie 50 gallon per day, and I make water for a 55, 30, and 15 gallon tank each week. I ran it for a 3 or 4 years without a booster pump. It was OK in the summer, REALLY slow in the cold weather... but it got the job done. Just this winter I put a booster pump on it and what a difference! I still don't have a pressure gauge anyplace. I don't really care what the pressure is. I did add an inline TDS meter a couple years ago. It's nice, bot essential, though.
My point is, you can get going with just the basics, and grow as you learn more. That goes for everything in this hobby. There are basic things you have to do to be successful. But just try to get those down pat, Then you can grow into more complex things.