The reason he gets fed up is because there is a limit to what you can do with MDF and inexpensive components. His design takes that limit into acount and that's why the size is the size.
J Klienbauer had a somewhat larger design, the routezilla.
In CNC all things become tradeoff's. You make it bigger you give something up...like rigidity for example.
I encourage you to build the machine according to the plan. There are enough hurdles to overcome without adding a few of your own.
Complete drive kits can be had from
www.xylotex.com, Hobby CNC, and a few other places. If you are worried about compatibility, purchase a complete kit.\
Demo's of all the software are out there, so you can try all these before you buy.
Good luck. It's a fun hobby.
Eric