@justus2342 I’m not aware of any design where the belts are out of the chamber. You would essentially need a hole the same size as the range of motion of the carriage, which is basically larger than the xy build volume. Moving the steppers out of the chamber is easy with a CoreXY design as you only need to holes to allow the belts to pass through. There are some pretty high temp belts out there.
The build chamber doesn’t really need to be overly hot. I’ve see some that claim 200C but I’m not sure I see why. Any thermoplastics on the market don’t need a chamber that hot. 70-110 is the hottest I seen a call for in any filament.
As for part cooling, yes you could eliminate the fan but it may not be a great idea. I’ve printed several parts in polycarbonate at 300C that still needed some part cooling. Usually only 10-30% fan speed and the “cooling” is being provided by 70C air. So it like cooling with a blow dryer. So if you do make a really hot build chamber you may need “cooling” to help solidify the part so it doesn’t just turn into a pile of goo.