He was a developmentally short napper from 3-5.5 months of age. We used holding through the jolts starting at the 35/40 minute mark into his nap and past the light sleep phase and into the next deep sleep phase of the next sleep cycle. So, yeah, minutes 35-1h for every nap except the catnap. It wasn't fun, but he was my only LO at the time, so I had the time and energy to do that. We also used the swaddle, white noise, and I still shielded his eyes when he was in REM so that there was no way he could see me.
No, he no longer needs his room darkened. I mean, we shut his blinds; but he could probably sleep with them open, too.
The way I see room darkening is that it's part of their sleeping environment. Just like temperature or white noise. We as adults have preferences, so why is it bad for our kids? I know some people who can sleep anywhere and others who need their own bed. Some have to have their covers just so. Some have to have it dark...so, if your LO likes to sleep in a dark room, I think that's okay
If you're worried it's a huge issue, then you can always try to make it less dark as time goes on. If you notice that it helps him take longer naps now, wait a few months, try just closing the blinds...baby steps.