Yes, it has been updated from beta that you can create as many worlds as your hard drive can hold (for an average hard drive, that's allot of worlds!)
Yes, I have a list of about 15 different worlds. I don't know the maximum.
Nothing will happen if you keep installing and uninstalling Minecraft. Minecraft does not track how many times you have installed it nor does track how many computers you have it installed on. The only drawback is if you uninstall Minecraft by deleting the .minecraft folder you will lose all of your saved worlds on that computer.
You can log into the Minecraft launcher on one PC with as many accounts as you want. You can also install as many as you want on each computer you have. However your saved games are not syced between PCs. On the same PC though, each launcher will still be able to access the same saved worlds.
You can find it on the Minecraft forums.
There are not many Beta servers up at the moment, but the ones that are can be found with Google. engamma.dyndns.org
The current version of Minecraft Beta costs £13.95 or $21.48 or €15.99 or YEN 1636.37
To do this you have to down date your minecraft version, there are many downgraders out there and then change to name of the file you have the world named to world 1
Yes you can, their worlds wont appear on your computer, all you have to do is download the minecraft application. there is no limit on how many users are on one account.
i dont think there is a compatible version of TMI for 1.2_01 :(
I know they can be found on beta and beta multi-player but I'm not sure if they are in alpha. Yes, they are in both to be sure get both alpha and beta although i would recommend beta cause it has wolves also alpha has been known to spawn SO MANY SLIMES its insane thats actually why i switche to beta
Go onto youtube, search toomanyitems 1.8.1, download it, then put all those files into your minecraft.jar.