travel most days with a bike on scotrail and never had a problem, even travelling late after a night ride. occasionally people will leave luggage/prams/golf clubs in the bike space, but as long as you ask nicely they will move them if needed. presuambly the bike watchers keep their wallets in their undercrackers and their house keys in their "special place". 😉
2 spaces per train IIRC
depends on the service (and type of train). the commuter train i get towards edinburgh in the morning normally has room for 8 officially on a 6 carriages. 3 carriage trains normally have 4 official spaces these days. guards are very good IME and unlikely to take action where more than 2 bikes unless the cyclists are being tits.