Suggestions for DIY Printer

Hello !!!! I am trying to DIY a printer thats based off the 3dp Unlimited Bench style printer. I have procured 5 x 1500mm (5ft) lead screw linear actuators. If you can provide some suggestions for me I will be super grateful!!

Motor: Came with nema 23's should I upgrade them to a larger one?
Structure: the lead screw rails seem a bit flimsy so I was thinking to reinforce with aluminum plates and brackets.
Motherboard: Here comes the tech question, which motherboard would support this build area? Arduino?
Extruder: so I am quite sure I need dual extruders, not going for super fine quality prints because we are aiming for size , which one would you recommend?
Heat Bed: So I was thining of using a tempered glass table at the base and diy the heat source, any recommendations there?
Any software suggestions would be greatly appreciated also!

So I guess everyone is gonna question why I need to build such a big printer, we are trying to build custom designed injection moulds for auto industry, hence the size. Any input would be greatly appreciated!

Sincerely,

Ken

well build area isn't an issue with the motherboard. You just tell the slicer how large it is.
With an area that large and big motors you might have power management issues.
How are you going to heat the bed ?
Or are you not going to bother with a heated bed.

I don't see how you're going to build injection molds out of thermoplastics, since they melt at about the same temperature as the stuff you're shooting into them. Who told you this was going to work?