I always ask myself what I want the bike to look/ride and feel like. Its all too easy to build a project the way you think people would build.
I try not to look at the builds on here, they only make me feel 'ordinary'
And ride whatever you build, ride it as much as possible
Pretty much this.
I don't build anything to original spec, I just don't see the point, as unless the frame is unique or very rare then all you are doing is reproducing a production bike of which there are already thousands of examples.
I always build from a bare frame and I usually start with the wheels, or at the very least get the frame on some wheels and then start trying different parts or colour combinations. My latest build is a 94 DeKerf Mountain. I had no idea what I wanted to do with it, but after a few experiments with wheels , stems and bars, I settled on an all black theme, as the frame is a darker shade of green. I think the bike's come out well and it rides like a dream.
If you can get an idea in your head of what the final outcome will be, be that upgraded but age related, or updated and with some or all modern running gear, then you can start to think about what parts will do the job, and don't be afraid to modernise, I have frames made in the early 90's wearing SRAM X0 / X9 2x10 running gear, and they ride fantastically.
Have fun with your build.
"Try not to punch any clowns"