If you are going to heat the print area to 50 or 70C, you want to get as much outside that area as you possibly can. That includes steppers. It certainly includes all the electronics. Unless you also want to heat up the room when you fire the beast up, count on having about 2 to 4" of insulation on all sides of the heated area.

A hepa filter is useless for plastic fumes. An activated carbon bed can do a pretty good job. It might be the size of a 20 gallon bucket and need to be steam purged on a regular basis. I have run some that were the size of a small house .... You could see us do the steam purge from 20 miles away ....

Bob