I'm not that closely linked to the selection side of things to really know the answer to how many will be sourced through CTC specifically given that the scheme is running over many FTOs. However, easyJet's current growth requires circa 850 pilots by the end of 2018.
As for of Brexit, this is something I'm following incredibly closely and as far as easyJet as a company is concerned they're effectively safeguarding themselves from this by splitting their UK business in to two. This would essentially mean another entity of the likes of easyJet Swiss whereby easyJet will register some of its' fleet and thus crew under the newly registered AOC. Which country this will be registered in remains to be seen, yet easyJet's Corporate press materials indicate they are now in the final stages of registration. It's worth noting that only 30% of easyJet's network of flights would be directly affected by Brexit and they are those which aren't covered within ICAO's freedoms of the air as a result of their intra-EU nature (i.e. Malpensa to Paris). With that said, whilst that safeguards the hulls themselves, it'll be down to the eventual Brexit discussions to establish which crew can operate them.
I wouldn't worry about something you can't control. Given easyJet's current actions towards Brexit it seems they've got their heads switched on with it. Who knows, it may just mean the Brits are kept in the UK bases and non-Brits moved to the rest of the network. But I don't think they're going to go anywhere anytime soon.