BBQ is a great idea. If her first birthday is anything like Ben or Oscar's she will be asleep for most of it Lol!
You can get Marquee's also from Bunnings that are very reasonably priced. We had one when we didn't have a pergola and it served it's purpose.
We only had family and close friends for all of our first birthdays..probably same for Tess
And the cake..well the decorations was for the baby and the first birthday picture, the cake itself was for the adults, chocolate mud
Just remember to enjoy Nae, it comes and goes soooo quickly.