Q: Stopping Apps installed on iPad appearing on iPod touch

If they automatically download when you buy them on the iPad then you should be able to turn that off via Settings > Store on the iPod (automatic downloads).

If they copy over when syncing to your computer, then with the iPod Touch connected to and selected on the left-hand side of your computer's iTunes, select the Apps tab on the right-hand side and untick 'automatically sync new apps' (which should be just below the box containing the list of apps).