i have to disagree, there are a LOT of nice horses in scotland. My most recent purchase is a scottish born and bred welsh D
the gems up here do go by word of mouth and through riding clubs and pony clubs. this one only recently caught my eye - what a super mare
http://www.horsemart.co.uk/advert/14_yrs_14_2_hh_black_aberdeenshire/83559
I guess the criteria for us purchasing our first horse was set by our parents. They were very insistant we could ride anything, hack anything, tackle an XC course and were profficient in stable chores. They were also very insistant we were prepared to do everything for our ponies. Working livery/full livery or loaning and sharing was never an option, even when i had 2 horses and was sitting my highers at school. was still up at 5am mucking out even before my finals. You sound like you've thought everything through thoroughly and planned everything which is excellent
i could never have a horse and let it go to an RS, it would break my heart but that's me. If you can cope with it, and seeing others on your 'baby' then it could be the perfect option.
Be very cautious with private sales. i will never purchase from a private seller. dealer or breeder for me as we were stung badly with a private seller who doped up for our viewing and vetting. get blood samples done, even if they are never tested at least having them in storage will give you comeback should things go belly up.