As far as extras, I got the black Friday deal for "the works." If I didn't get that, I would purchased floor mat and shoes from Amazon. You don't need their heart monitor (I do use it though) and the earphones are not used (I use airpods). I did buy toe cages ($35) for the kids because I wasn't sure they would ride very much, and didn't want to invest in shoes.
Other extras would be a plywood board if on carpet ($50 max), fan, and weights. There are other things I bought to make life nicer, but not necessary. Also tip for delivery if you wish.
If you do buy through Peloton, you can finance the whole purchase--bike, shoes, extras at 0%