Jonny,
Castle Coombe was the first trackday I did - great fun, VERY fast. Don't strain the engine. It's very tempting to keep your foot hard down on the straights, and you can hit the rev limit rather too often.
I doubt there is any need to take new pads, a Seven is not a car to wear them out very quickly, and Castle Coombe is not a track that requires extensive use of breaks.
Start gently, work up the pace. Don't worry if the world seems to be going past, just have fun.
Try and get a ride with someone who knows how its done, it can be a real eye opener. I was taken round by Barry Williams (long time racing driver including Le Mans) and while it didn't feel fast, it was, but it was very very smooth - something I spent the rest of the day trying to achieve.
Above all, enjoy it. Its a great buzz to get a corner right, and the grin just gets bigger.
Dave H