Sorry about the delay in replying here - I cant offer any advice about building up a bike for triathlons that any cyclist couldnt answer better - a bike is a bike is a bike and triathletes generally dont know an awful lot about bikes or riding them!! Check out the Scottish Triathlon Association website for races and links, and go shopping at Edinburgh bicycle works if you want fancy clothing.
Thats my advice, for what its worth!
Kelly
PS it is worth joining the STA if you are likely to do 3 races or more - you get subsidised race entry fees, some insurance cover and automatic entry into the STA rankings.