I am in the same position as you as I am 20, and building my own boarding stables too! I have financial backing from a very wealthy friend as they know id like to one day turn it into a charity for abused horses...
I began with 2 lists.
1 list for a yard already built
Second list for 'virgin' land.
You have to think about, water supplies, electricity supplies.. drainage/sewage.. do the local authorities give permissions for such utilities? Planning permission for your barn and living quarters??
Then you need to think about the stables. What size, what design? Are you going to provide toilets and an area inside to make a drink or change clothes? Tack room.. separate or built into the back of each individual stable? Feed room, separate or added to stable? Paddock.. drainage, fencing, surface material, flood lit? Grazing.. quarantine stables, quarantine grazing.. will there be enough grazing for summer and winter turn out.. bedding storage and hay storage.. yard security.. if need be, any heavy machinery for the up keep, ie. Tractors..
I had a long think with pen and paper infront of me of what I would want if I was on a yard. Things I have missed or wanted when I been stable renting..
Then I googled equestrian contractors, for my stables and paddock. Got a few quotes and now im deciding with my business partner who to go with
Hope this helps ! Xx