I'm planning to join all the factions with my 1st character.

I'll be joining all the faction I'm able to with my first character. I get around this by RP'ing a power hungry character. With that said I haven't decided on Imperials or Stormcloaks since you can only choose one or the other. After that I may play more singular characters, like a full blown mage that ONLY does the mage guild and maybe Imp/Storm (w/e I didn't pick before).

Why not. I might do the Companions, the Thieves, Dark Brotherhood and College of Winterhold all on the same character. It makes the character even more strong, and it has nothing to do with wanting to choose a path. Since Skyrim is made so you basically can play whatever you want to play, it doesn't really matter if you are a mage and join the dark brotherhood. If you complete all of the factions, it makes you a more respected character and I really can't see any disadvantages in that. People might say that they don't want to rush it all on one character, but Alas, it takes time even if you are on the same character. It can be years apart, your longlasted mage might have turned into the dark arts and joins the Dark Brotherhood for support.

The experience becomes what you make it.

Probably not. I did that in Oblivion, but it felt strange that one person was the leader of all major factions in the game.
This time around I'll only join factions that make sense for my characters to join.