1) sometimes they open early, soemtimes they don’t – I wouldn’t gamble on going before, you can climb of course, but sod that.
2) no idea, it’s a shit drive, I’d rather get it done with. Leave before dawn, get there for dinner.
3) There’s loads of threads, but:
Try not do drag brake down the trails, it cooks your brakes and eats pads.
It rains a lot, sometimes you’re lucky, sometimes it rains every day. Take clothes / tyres to reflect that. If you’re new to steeper stuff, take lots of brake pads.
Try not to bin it on day 1, spending days sulking around the digs whilst your mates ride sucks, done it twice.
Get some gravity experience if you don’t have already, it a lot steeper than the UK by and large, the trails are longer.