I'm able to purchase a house in Whiterun (which I haven't done, much prefer my abandoned shack) and that's as far as it goes, and aside from never being able to FUS RO DAH, is there any other restriction I don't know about? I mainly am doing this so that my character isn't all Dovakiin'd out and regarded as the chosen one, and more of an unknown assassin. Hangin' with the Greybeards just ain't my style.

Hanging out with the Greybeards is only a small portion of the main quest, I don't see a reason not to do it

well youve already done the only quest that really has some drawbacks to not doing, so your fine.

no dragons, no shouts-thats about it

I know, I completed it on my first character. Was more or less a joke.

i usually stop before i get the Horn quest for the shouts

You won't be able to go into certain tombs because they need a key. When you finally do the main quest you will likely be inordinately overleveled and overgeared and feel you broke the game's difficulty. It is possible that you will find quest items and be unable to turn them in to the correct actor. You will not complete a certain collection quest without the main quest. You won't learn some other interesting shouts besides fus ro dah. And finally, never-ending dragons to punish you for fast travel.

Your just missing out on fighting dragons

DRAGONREND

While it's not possible to unlock shouts,dragons don't appear randomly and I consider this a major point in favor of NOT taking the main quest.

longer game duration...I know.