The only real "gotcha" that I can think of is that bolts are sized nominally and the claimed size is not the actual size. Where this becomes relevant is the pivoting drive assemblies. The undersized nature of bolts when fitted into bearings or sleeves may create too much slop in the system and this is something best worked through before you get to that point. As far as the remainder of the system, resist the temptation to jack the X-axis way up and reach back down with a long Z like the guy did in the video. This just introduces unnecessary leverage into the system which leads to inaccuracy in the cuts and unnecessary strain and wear on the bearings. Keep the system as low and lean as possible, building it for what you intend to use it for not what you "might someday" use it for as you'll get better long term results. If you do feel the need to build the might factor in, just leave the vertical parts of the assembly a bit longer and add a set of high and low stops to the side posts to where you can still easily raise the gantry should the need arise. While a wood base is a perfectly workable solution, remember wood changes dimensionally with variation In moisture content so account for it. The big issue is going to be the spoils board due to it's size so make sure any size changes don't affect machine alignment. Looks like a nice project. Please keep us informed on the progress.
If It weren't for the size of the system, I'd recommend a two plate system with the pulley sandwiched between two plates rotating on a simple dowel and bearing axis but I'm not sure set screws tightened into ground flats on dowels will have sufficient strength on a larger system. (If you didn't quite follow that here is a similar example, one that I have actually morphed to use on a R&P system in another drawing but I'm a hundred miles from the computer that the drawing is on at the moment so I can't offer it up.) If you do think you can get set screws to hold, it provides a much simpler solution that the average person can copy without the need for a lathe.
