Never tried using ball bearings on extrusions.. the tolerances of the extrusions will be important to know BEFORE buying material. I used 12mm rods on my large 450x450mm bed printer. I used 4 cheap MK2 heat bed boards bonded to a large 3mm thick aluminum sheet, with 0.5mm thick PEI film bonded to the top.. backside is insulated with 2 layers of cheap foam board bonded on too. I found a $15 used HP Server power supply on Amazon to power those boards (12v and up to 60 amps).. thing heats up faster than any printer I have. print bed is light enough for a single high torque NEMA17 motor... and I use only steel corded GT2 belts.
One lesson learned with E3D Volcano... my is 12v .. does not have enough power to extrude material fast enough to use a nozzle bigger than 0.8mm with 0.3mm layer height. If ya want to print material really fast, just a 30 or 40W heater cartridge isn't going to cut it.. probably want twice that. I was going to make a heater block with two heater cartridges in it.
Also, IMO.. bed leveling is a must, since the bed is so large... I'm using a BL-Touch sensor.
The idea of using pellets for printing is a great goal ... because material cost using fliament is a killer for many projects.. I'm printing a lot of parts that use an entire 1KG reel.. and some designs that need more than 1KG, and I can't print them .. so a way to hopper up 1-2 KG of pellets would be cool.