Birthday madness

I'm in the process of planning Ari's 2nd birthday party. My first attempt at a guest list has come up with an absurd number of potential partygoers. Yikes.
Both Rob and I are nervous party hosts and Ari's first birthday did little to alleviate this. After erecting a sunshade and preparing a BBQ lunch, it proceeded to pour buckets of rain ALL DAY.
By mid-afternoon, our house resembled a nightclub, we had so many people crammed in. It was a great day and Ari had a blast, but the rain thing was a bit of a bummer.
This time around, my aims are simple. That we invite everyone we want to and that it requires as little work as possible, so we can actually talk to our guests.
So a morning tea in the park next to an ace playground is what we are thinking. Now all we have to do is pray for NO rain...