I'm a hu nl player and I usually play something in between 30k and 40k hands a month at midstakes. If you play lowstakes over 40k hands/month is easily achieveable i think.
I get most of my volume on stars but bumhunt across a couple of other sites.
Winrate over 200k hands sample is 17bb/100 but it's probably a bit higher than my real winrate cause I've been running pretty hot overall.
Rakeback doesn't depend on the game you play but the site you play on/the rb deal you may have there, but I think in plo you will pay more rake in general since less hands end preflop and therefore more hands get raked.
hope i could help :)

well it obv depends on how much action you get, but starting with 1 table seems very good.
maybe add another one when you start feeling more comfortable, but in order to improve your game you should always try to play few tables, 1 is certainly best for a start.