I'd appreciate any advice or tips!! I'm hosting an at-home 80th birthday party for my amazing mom.

For my grandmother's big birthday her daughters made a timeline of her life with copies of pictures of various stages. It was really sweet and made a good conversation piece for people to ask her about various events and places she had been.
This was also a surprise party - she knew she was having a little party, but the arrival of her kids from out of state was a surprise and she was thrilled. Maybe you can soften the surprise just a little....50 people jumping out to yell surprise is a bit startling at any age.
This white bean and fennel dip is cheap and delicious with bread http://www.food52.com/recipes/8908_roasted_fennel_white_bean_dip

As far as decorating, I'd go for a combo of flowers and framed pictures.

All of these are great and easy ideas:http://food52.com/blog/4951_7_lowmaintenance_hors_doeuvres

First, I veto anything with prunes! Even though they are delicious, the implications may not be what you want for this occasion.
I would think of nostalgia foods. Are there foods she made for the family that are especially loved (that would suit this kind of gathering). Does she have a recipe box or Betty Crocker Cookbook that you can borrow for ideas? Here's a recipe from my mother-in-law, born in 1917 -- http://www.food52.com/recipes/18495_bunnys_broiled_egg_sandwiches, that might work for you.

I would have trays of one-bite appetizers that are not too spicy and easy to digest. Lightly toast some bread, cut off the crust and cut into 1" squares, top with devilled egg, or a slice of cold cut meat with a dab of mayo, or whatever your imagination dictates. Even a cracker with a smear of cream cheese and slice of prune is nice. And a cake with one of those candles that never blows out.!

Look at the recipes from here and see what you think she'll like. http://www.food52.com/contests/194_your_best_open_house_dish
Birthday cake and coffee work, too. For my mother's 80th, we did a slide show of photos interspersed with some of her more pithy quotes (there are a lot of them.). We ran that on a large screen TV in the background. It was all the decoration we needed.