As for 6-max vs. full ring I did actually write, that I think, full ring tend to be softer at a given limit. In fact this is the main reason, I keep gravitating back to full ring, even I was planning to get more into 6-max, when I moved to 888 poker 4-5 month ago.
But most of the time, when I jump onto a 6-max table on 888 Poker, it turns out, I am playing with 5 regulars, or there are 4 regulars and 1 fish, who is on my direct left forcing me to play most pots out of position. Neither of these situations are profitable, so I end up moving back to full ring, where if nothing else most tables feature a bunch of bad regs, that are easily exploitable.
Therefor it was perhaps a bit misleading to say, its easier to move one way than the other. If full ring is actually softer, and of course this is difficult to prove scientifically without huge samples, then a good 6-max player will do just fine at full ring after learning to fold a bit more against EP opens.
I still think, it makes sense to start at full ring though, since it teach you a lot of good habits like patience and folding. And if at some point you want to move into tournaments or live poker, you need to learn full ring, because these games still mostly play in that format.
But that being said, if someone just enjoy 6-max much more, then I would let that be the deciding factor. If you are new to poker, you are probably playing at least partly recreationally, and then there is no point in forcing yourself to do something, you do not enjoy.