Usually no, most will either crash minecraft or will not work.
You have to wait for the Mod maker to update to the latest version of Minecraft unless they say other wise.
It may take a few hours or a few weeks to update mods.
The mod developer will need to update the mod to be compatible with the new Minecraft version.
You have to download the TooManyItems Mod for Minecraft. Search it up on the forums and download the ones that correspond with your minecraft version. When you update minecraft your Mods wont work because they will become and old version so wait for the mod maker to release a new version of the mod that works with the new version.
As of 1.7.2, the Minecraft mods currently available can only be updated after a new version release. Mojang plans to make the source code available to modders in the future for later released. When? No one knows.
Yes. Most mods in Minecraft are free, however you can donate to the developer to help them improve and make new mods.
Wait for the creator of the texture pack to properly update it the latest version.
If you had a 1.3.2 mod and you want it to be in 1.4.2, you have to download the mod again when it's uploaded. If you don't use the correct update for the minecraft version, your minecraft will crash and you will have to force update it which makes a new minecraft jar.
Yes, depending on your current version of Minecraft, you can update it to completely start on a new slate (deletes all modifications). Or, you can open the minecraft.jar file using Winrar and manually undo what you replace. Or even un-install minecraft and re-install it using your previous licence.
To enhance the game, and add new things into it.
no you can't, mods are for PC only.
If you get bored of Minecraft, you can always download a few mods, get a new texture pack, or go on a server and play with friends.
If you mean in all mods ever, then potentially thousands. Mods are add-ons to Minecraft created by users, and new ones are made every day. To count how many modded mobs there are in Minecraft would be near impossible
Mods are Minecraft 'modifications' that people have made. They can be simple things like new creatures or new tools, or they can be complex, like expanded redstone functions, new dimensions like the Aether, etc.