Whereabouts are you? Innerleithen has the best enduro scene in the uk, really varied events, excellent routes, winter series, the gravity enduro tour comes by once a year, even got a world series round next year... But just about everywhere has enduro events these says, it's ace.
Hardtail- I used mine for half of a UKGE round before the forks spat the dummy, it was absolutely fine- a wee bit slower as you'd expect but no increased risk of death.
Fullface- most UK events don't need it, you might want to choose one but there can be rules drawbacks (in the UKGE, you need to wear a helmet at all times, so if you choose a fullface for the descents you either need to wear it on the climbs or carry 2 helmets, both of which are annoying). Personally I don't think full face is the right choice for this sort of riding, I overheat and end up distracted and more likely to crash!
But ymmv. If you do go full face get a well vented one, Urge make some very suitable ones for pretty good prices. My old cheap 661 was horrible for enduro, basically a sweatbox.