1) No. Cons outweight the pros.
2) When it comes to customs, the only things you can transfer to an alt at this point are tokens outright. And in the long run, you're transfering time from one character to the other in terms of questing. As long as customs remain owned, then it'd probably be relatively alright... in general... but I still don't like multiplaying.
As for why I don't like multiplaying, it can encourage a more solo-ist mindset. All you need to level now is your cadre of alts who are moderately amped on customs. There's no point to interact with others to group ... but, that's also an existing problem as is, because of the level range and the rarity of people, sure. With alt-armies, comes control over legendary spawns, which admittedly, most of us who can kill them invite others when we can/know they're around. With your army of alts, why bother with others?
An army of alts is sort of like an artificial solution to a less-busy-looking-mud. Yes, it looks like there are more people, but it's more akin to a MMO where one player is an actual person, and three of the others are farm bots. It looks like there's a bunch of people, but 75% of them aren't even actually -there-. So, nah. MMOs generally don't allow you to log multiple characters at once, obviously, people can and do get around it, but by default, you usually(usually) can't open more than one instance per computer... and if you have two or three, well... then, you're rich to start with >P
So... No.