Congratulations on getting started on your machine, and thanks for the compliments. You will get plenty of help and comments here. Sometimes more than you may be able to handle.
One advantage of the 50" width of cut on my machine is that I don't need to use the table saw so much anymore. It can sever cut a full sheet of MDF with simple keyboard jogs. Making yours wider (if you have the space) will cost more but is well worth it in the long run. I will rarely, if ever, need the extra 4' length over the full 8' sheet capacity, but the cost was negligible, and there is a nice built-in 4'x4' worktable on the end of the machine that I use for that purpose quite a lot.
Good luck with your build. Ahren's site has CAD drawings of the carriages and R&P drives that you will find to be useful during your build.