Anyone have some 2nd Birthday Party advice?

I have a daughter who will be 2 next month. The sad thing is, since I'm a SAHM, and she doesn't have siblings near her age, she doesn't really have any friends. Sometimes she'll play with other kids on the playground, but we've never become friendly, really, with any of them. I do have two coworkers who each have kids about her age. She's met them once or twice, but is kind of shy and doesn't really go for being pushed to play with these kids and will just cling to me when they're around.

We have this place called Big Bounce that is just those big blow-up castles and things like that. They do birthday parties for $100, which include 8 kids, balloons, 2 hour party room, and unlimited play that day on their bouncy toys and mini golf.

These coworkers each have 3 kids. The oldest is 7. I'm wondering if it would be a good idea to try to have a party, spend the money, and invite these guys, since my daughter is so shy and unsure around what are basically strangers. Or should I just have them all in the backyard and grill (it should still be in the 60's in early November in this part of the country) and do cake?

On her first birthday, we just did a cake and had video chats with her grandparents. We could do that again this year.

What's your experience with 2nd birthdays? One friend told me that starting with big parties this early will just make them EXPECT it every year. On the other hand, we might not be able to do it every year, and might be missing the opportunity to give a big party the one year we CAN afford it.

Also, what do parents of invitees expect at birthday parties? I've never done this before, so I don't really know what to do as far as invitations, etc. The food would just be cake and ice cream, and pizza. But should I do some sort of favor/gift bag, or what?

Thanks for your input and advice.