Bikes count as their own baggage so you pay whatever the fee is for “1 bike bag” and that is allowed to weigh up to 32kg. You then have your normal hold baggage, hand baggage etc on top of that.
I flew with them last week (as well as many times before) and I’ve never had a problem with EasyJet. Last week’s trip was very smooth, bikes were waiting for us almost before we came through passport control, all bikes survived fine with no injuries!
In theory, you’re only supposed to have the bike in the bag but I’ve always filled it with clothes, tools, helmet etc and never been questioned over it.
It’s worth printing out the T&C’s from EasyJet’s website and highlighting the bit about bikes though, just in case.