In order of question:
- just gPay contactless payments (that I've found)
- me too, no issues
- should play just fine with gPlay
- updates are ota just like stock android (once gos is initially installed); they have a restore method that afaik uses the google restore website, I haven't used it in a while but it does work and is pretty straightforward
(used many, many roms over the years, currently gos for 3.5y)