1. Some find it good, some not. Its a matter of preference only YOU can answer for yourself once you have the phone.
2. No. But as stated above, with Android 4.0 you have access to the entire internal memory for storing apps. So what you should do is make sure that the Android you are getting is using Android 4.0, or if you can only afford something running Android 2.3, check if it is upgradable. Failing that, make sure it has at least 3GB of onboard storage.
3. Because its newer and better. Android 4.0 has more features, has certain apps that only work with 4.0 and higher (like Chrome), and is generally faster on the same hardware. I can throw the question back at you. Would you rather buy a laptop running Windows XP, or one that runs Windows 7? I'd think you'd answer that you'd get the one with the newer Windows.