I would like to add that in terms of precision welds, I am most likely going to be taking the parts to a machine shop where they will have all the nessesary jigs and fixtures to avoid distortion if i were to tackle this myself.
you dont need to be to exreem about the wields, as long as its sort of level on the top, and measures square ( you will see any twists when cutting the steel into parts, its easy to avoid any visible distortions, just use the best bits for the top ). I did the same as your suggesting though, i got a firm to do the welding, after i had cut and marked the pieces.

Epoxy does most of the rest,