The social niceties of being four

Isabel's birthday is coming up in August and, being the youngest child in the year, she's been to several birthday parties during the course of this school year. We're now planning hers, and I'm starting to realise that there is a large range of social pitfalls which we need to negotiate now that she's in school. Life was much easier when she was younger. Those I've identified so far include:

1. Venue: she's really enjoyed a couple of the parties, and requested the same party for herself. We went to one in a local soft play centre last week which was great (possibly because it was on a Friday and therefore empty - she and her friends had a school INSET day but everyone else was still in school!) and I've now booked hers in the same location. Does that make me a copycat? I think I may just have to suck that up - as the last birthday of the school year I suspect this may happen more than once over the course of the next few years!
2. Invitees: I had a long conversation with a neighbour about this recently to try to understand who you're meant to invite to these things. Several parties so far have been for the whole class, but since the soft play party is £11.50 per child that's going to bankrupt us. Result - someone's going to be insulted. Again, I think I'm just going to have to suck that up. Or suck up to the bank manager. Either way, a lot of sucking is going to have to take place!
3. Party bags: Do I go educational (a nice book!) and impress the parents, or buy cracker-filler crap and impress the kids? Or a combo of the two? Either way, that's another addition to the total bill...

Actually, all I really want can be summed up in two points: that Isabel has a good time, and that I don't bankrupt myself. At least the cake's sorted: CostCo does a delicious and large cake, which you can have personalised, for about £12, and it feeds at least 30 people. And that's my top tip for the day!