I'd stick with a foam long board the first few times till you get pretty solid at standing. Then after 2/3 times out, go out for an hour on a foam board then switch to a hard longboard. Once you get used to that... then you can go to a shortboard. Shortboards are quite a bit more difficult. My sis has a foam and hard long board and I always need to take out the foam board the first day or two before I try for the hard. I can't handle her shortboard for the life of me.
Best of luck with it though. Even sucking at it, I still have a ton of fun.