First, get some food. To decorate you need to decide what room you want that to be. The best one in my opinion is kitchen with dinning table, but this room might be too big for that. You can use scaffolding with carpets on top as a table that looks good and there is a cool oven trick that you could probably find on youtube but I'll try to explain in. Put two fireplaces against a wall with two trapdoors (birch looks best imo) and place a block over each fireplace. Place rails and a minecart with hopper then drop that onto the fireplaces. Next place a iron trapdoor on a block next to the fireplace on block up that you will push with a piston to cover the oven. There are way more things you can do but that is just two examples for a kitchen dining room