3Drag / K8200 redesign sketch, prusa-like design

I own a 3Drag, and there are some things that I hate in this printer:
- with a 3 mm glass on the print bed, the X axis weighs 1.7 kilograms! the printer shakes a lot while making fast accelerations on the X axis
- no belt tensioners
- only one threaded rod on one side
- the back of the bed is not insulated
- non-standard hole spacing on the extruder mount (an E3D hotend is the best upgrade for this printer IMHO)
- default extruder can't handle flexible filaments
- every M8 thr