You can take more cabin baggage on board BA Euroflyer, Easyjet incredibly strict with sizing in the cabin and will charge if an inch to big.Nothing wrong with Easyjet at all. Better than BA for short haul these days imo
Case under seat size is pretty small but if you’ve checked that will be fine
Boarding passes fine, but definitely worth having the app on your phone if you can as you can have them on there, and it also gives you real-time notifications with things like gate number, boarding and any delays.
90 mins is fine.
Yes, straight through security unless you’re checking in luggage
Coat - yes you can
rather fly BA personally.