Helmets are a hire from KH (fiver I think).
As for speed - just get out there and don't be an arse - that's all anyone expects. There are always slower drivers, as long as there is some consideration for the guys overtaking, *nobody* will have a problem with that. (plus, if you let faster guys past, you can try to copy them and see where you're slower)
If it's your first day - I'd probably recommend booking just the afternoon and blagging as many pax laps in the morning as possible. That means you've got used to where the track goes and you know what the car can actually do.
Then just build up speed - don't try to be quick from the start, concentrate on keeping a good line and the speed will come. Get some of the more experienced guys to pax with you and give you pointers, if you fancy - I found that really helped too.
At the end of the day, it's no more challenging than a road run and a bloody sight safer
