My baby's christening is turning into a wedding? What's the dos and the don't?

Basically it started off with a pretty large baby shower- with everyone excepting to be invited to the christening and now my mom has mention that relatives were mad they were not invited to the shower and my mom promised them invites to the Christening. So when all is said and done, it's going to be like 100 people/kids- the same as my wedding!! LOL My family is really helping- my mom volunteered to cook all the food if need and my sister is using her connections to wrangle me up a hall at a community center using her friend. Due to the size of this- I decided to have the baby baptized at 3 months to give myself a breather. Now I am wondering should I have a DJ or music....I think we will do beer and wine with a buffet. Paper plates and plastic cups- very casual. But do I need centerpieces? Favors? How casual can I do it without it being tacky?? There are lots of website to help plan weddings but I can't find anything for a large christening! Any advice would be great since this is my first! PS- all the family excitement is that this is the first christening that anyone has had for like 10 years and my family is use to them being very fancy catholic over the top type of deals but we are having her christened "all faith" like myself :)