Before we moved we hosted the neighborhood Xmas party. No matter what fancy food I served (smoked salmon, brie, prosciutto, etc) everyone loved my meatballs, which are super easy. I just used meatballs from Costco, then you mix equal parts grape jelly and BBC sauce. Sounds yucky, but everyone loved it, especially the guys. Keep it simple, I like a spiral sliced ham, Honey baked if you can afford it, otherwise I am sure Costco has them. You don't need to bake, just let it come to room temperature. It's foolproof. Some dinner rolls, and a few side salads, and you are good to go. For dessert, pumpkin pie is always popular, cheesecake too, but it is more expensive. Some kind of punch always goes well. Hot spiced cider, or hot cocoa is also popular. Serve the cocoa with a candy cane.
For cheap decor, go to a Christmas tree lot and ask for their clippings, they will usually give them to you for free, they trim the trees up a bit on the bottom for the customers. These are only good for a few days because they dry out, but they look festive and smell heavenly. Just spread this out on the buffet and dining tables and tuck some nice wired Xmas ribbon in and around. I think you can get a huge spool at Costco for $10. A few ornaments here and there will add some color (you can find them super cheap at the thrift store, like 25 for $1.99.) An easy way to make the food look better is to elevate some of the dishes. I use a cardboard boxes covered in Xmas paper, use several different sizes. This adds dimension and makes everything more appealing, and easier to get at.
If you have tables for people to sit to eat, put the cutlery and napkins at the table in a pretty Xmas basket, that saves people trying to hold them while they fill their plates.
If you have the budget, get a Santa. My husband has done it many times, at our parties and at his work. If you can't afford a professional , you can get Santa suits for pretty cheap, less than $100, try Target. Kids love that. I made goodie bags with small toys, Xmas stickers, candy, peppermint sticks, etc., but really they cared more about Santa. Our last year before the move, one of the kids said for Christmas he wanted Chip and Lisa not to move - it broke my heart. They all knew it was my husband, but it made it almost better for them.
Good luck and Merry Christmas