Definately RO.
If you don't, you'll get through so much resin!
Depending on how much water you want to filter per week, you'll need an ro to suit.
However, from your motto about wanting to be a millionnaire, I'd buy the best and biggest you can afford, so you don't outgrow your equipment too quickly.
So why not go for a 40 40 ro?
Then your resin will last ages, as it's only polishing out the last few ppm left after the ro.