Ventilation is mostly important indoors (housing) to avoid the fumes and smells to be inhaled
Regarding the laser itself depends greatly on what materials you will be engraving
Assuming you do not do plastics, which are toxic for YOU and the machine, i would recomend maybe if you plan to do a lot of cutting air assist to keep the lense clean as much as possible.
Regarding temperatures. The extremes are complex. Not because of the laser itself but the static charge that might build up on the frame on very low temperatures (-3ºc here atm for example)
Nothing grounding the frame wont fix
I believe the biggest element of disconfort on low temperatures tends to be the Human factor. At <30 you will freeze