Embarking on a very similar adventure ourselves; Cambridgeshire and the "rat race", to (slightly higher than you guys) North West Scotland.
Funny, the amount of people who keep saying how "brave" we are. Some might say they are braver staying, with all the risks of pollution, over-population, unknown & processed food and screen-zombie syndrome!

Visited Mull a couple of years ago, right at the end of the Ross - Iona etc. A very beautiful place.
Sounds like a similar plan to us - with the chickens and goats. Plus growing as much as we can. Not sure if you've thought about it too, but we are going to offer some holiday accommodation (a yurt and camping), to top up the 'pot'.
When are you hoping to move? Everything (well almost) is in place for us to move on 1st April - thought that an apt date!

If you are interested, and because I am a relentless plugger (sorry), I'm writing a blog of our preparations and experiences (at
www.offgrid-online.co.uk). Would be great if you added your thoughts, experiences and preparations to it all too...

Good luck.