Coffee roaster here, at 350F the beans have turned yellow and barely started browning. 390F~ is around the point where most roasters would consider development of flavor to really take off (yeah yeah pre-development phase, I'm keeping it short) and beans will be done at various points after that depending on roast preference.

The smoke that the roaster produces towards the end of roast is no joke, and some has to get on the beans, but I'd say it is minimal enough to not be an issue as there should be plenty of air flowing through the roaster at that point.

If roasted improperly oils could seep out of the beans while in the roaster which burn as well and stick to the beans. I'd say that is more of an issue than the smoke or roasting too dark.

350f sounds too low to me. First crack (beginning of a very light roast) is around 200c/392f. Most coffee is roasted quite a bit darker than that - e.g. 220c and above

https://en.wikipedia.org/wiki/Coffee_roasting

but the coffee turns very dark in some roast and it generates a lot of smokes during the process.