I took the iPad around with me all over the US west coast last December. To answer your questions:
a. Depends on which iPad you get. If you get a 3G iPad, then you should be getting a micro-SIM and data plan with one of the telcos (in the same way you'd get a SIM and a plan for a mobile phone.) If you get a Wifi-only iPad, then you'd need to create a wireless hotspot. If you already have a USB broadband modem, you can get a wireless router, into which you can plug the modem, to create a hotspot so that your iPad (and other Wifi-capable devices) can join. For example,
something like this. (This is from Three Australia, for example.)
b. You should be able to access Wifi in most hotels and some cafes and hotspots, either free or for a charge. It helps to research in advance the cities you're visiting and hotels you're staying, so that you know where you can hook up with the Wifi. Some chain stores like Maccas may offer free Wifi, but bearing in mind the service at these outlets can be quite flaky.
c. Plenty, but you need to be more specific about what exactly you want to "do".
d. Yes, you can Skype. However, you will be able to see the incoming video, but the party at the other end can only hear your voice (as the iPad has no support for video camera.)