Connect to the iTunes Store and a link to the App Store can be found centre top of the Store's window.
All iPod apps are from iTunes.
Nope, no sharing apps.
no you cannot use ipod and iphone apps on itunes, but you can buy the apps on itunes and put them on your ipod and iphone
The apps should not disappear from your iTunes account.
you can search any apps on iTunes or see apps on the home page on iTunes
No, you just need to free download iTunes and then use it to buy apps. iTunes is free.
They shouldn't be; apps are tied to the device and the Apple account, rather than iTunes.
You buy apps at itunes.
You can but I don't recommend it, because you won't be able to have apps from multiple itunes acct and you have to make a new account, to download the apps.
Restore them. Click apps on your iTunes and out the apps back on. Any if then that aren't in iTunes, just download them again.
With the iPod connected to iTunes and selected in the left hand pane there are a row of buttons (Music, Photos, Apps etc.) across the top of the right hand section. Clicking the Apps button will allow you to Sync your Apps with iTunes.
Click on the IPod symbol, when you plug it in, on itunes. Up top go to "Apps" and select "Sync Apps" off to not sync them :)