Hi Shaun,
Welcome to the forum you'll find plenty of help and advice on here from past builders of the Mazda SDV's including from myself, and there's a whole wealth of info in the archives. You can find all my build photos at http://www.mx5westfield.co.uk
Just to give you a quick heads up that there's a few small errors in the build manual and things that could be done slightly differently to improve the build. This thread will give you a few pointers to save any mistakes http://forum.wscc.co.uk/forum/index.php/topic/98062-updating-the-mazda-sdv-build-manual/?p=1000978 also should you have any questions during the build just ask on here
Regarding the cost of the completion kit, for the parts included it actually represents very good value and its price is discounted compared to buying the parts individually. I built mine from only a starter kit as I wanted to change a few things but it did cost me a lot more to do things this in way, in hindsight I should have bought the completion kit and saved a few £££. If you decide there is a few parts you want to get from somewhere else then Westfield will adjust the contents of the completion kit and take out the parts you don't want to make the price a little bit cheeper for you.