Plockton is lovely, but for your first trips around Scotland I'd recommend somewhere easy like Perth or Oban. Both very nice in their own ways and you'll get a warm welcome at either place.
You can get fuel easily too, which can sometimes be an issue at other places.
Do be extremely careful of the weather and the hills. As you have trained in and around London and the South East, the differences and risks involved in flying up here are marked. I'm assuming you'll be flying with the peeps at Highland and if so you'll be in extremely safe hands.
Wherever you fly to, all of a sudden you'll find flying down south very boring after experiencing what Scotland has to offer. On a good day it's breathtaking. On a bad day however it can be really nasty, but one good day can make it all seem worth it. (Well that's what I keep telling myself!)