I'm guessing from your signature that you'll be flying from the NorthEast to Amsterdam to somewhere a lot, so you will be soon familiar with the D6 circus, especially at peak times. Suppose you will have a choice of Newcastle or Durham Tees Valley (or MSG as it was known when I was a lad).
As for the miles, they are worth collecting, but "free flights" is a bit of a misnomer, the taxes are often more than you can get a discounted fare for anyway. Level miles, as opposed to award miles are collected and help move you up that ladder, towards your lifetime Platinum status.
Good luck, and welcome.