It is up to you whether to use integer or guid ids in a custom feature. One advantage of guids in mojoPortal is that they enable you to utilize some sub systems like ContentRatings, Content History, and other planned sub systems because you can store and retrieve items from those sub systems using your item guid. So if you want to use those subsystems then guid has an advantage. Of course if you still would rather use an integer, you can do that but also add a unique indexed guid column as an alternate key then you can still get the benefits of a guid. Integers can be a little faster when joining large tables, so if your feature is going to have multiple tables to join with millions of rows then integers might be better.
Hope it helps,
Joe