Positives/Negatives to a H-Bot / CoreXY drive mechanism?
Low moving mass allows higher speed / acceleration while maintaining precision.
Long, complicated belt paths add complexity.
Build size recommendations, the plan is larger than 8x8x8"
My ~6.5" square bed is usually enough. I would like larger, though. If you're designing your own, 12"x12"x16" seems reasonable.
# of extruders and wade or direct or combination
I have one extruder. I assume "wade" means Bowden? Mine is Bowden. Different people have different needs, but I'd generally recommend one direct, plus one Bowden if you can afford the extra hardware.
Control board?
Smoothie or Duet. If you can't affort $100+, get a $55 MKS SBASE -- I've had great experiences with clones.
Enclosure built in or open design?
Yes, enclose it!
Any other recommendations or requirements people would want in a printer?
Rock-solid frame. Should be metal, welded or bolted to metal.
Rigid, supported linear motion -- NOT RODS! Rods bend, a lot. Supported rods (e.g. SBR16) are good for high force, rectangular guides (e.g. SR15) are good for light weight.
Heated bed, ideally machined aluminum topped with PEI.
Don't bother with an LCD, just use the built-in ethernet on the control board.