Some species can be started in summer. I've had success with ficus. Great practice material. And elm.
Clear plastic to see roots, but wrap with foil shiny side out to keep temps regulated, leave a peice you can remove to check for roots.
Black plastic will likely build heat and rot something. It seems folks who use pots have their technique and timing down, so they don't need to check for roots.
A syringe for watering, so it can stay tight and closed, is the best idea I've read. Far as how often, like everything else In Bonsai, should be checked daily until you know for sure. Damp, but not wet.
I would say have at least three successes with test material before cutting into anything you really want to suceed.
And long stranded sphagnum is definitely superior!
Some pics, cuz its easy, not cuz they're necessarily helpful. Five on a Ficus. An elm. Just for practice, all successful, until aftercare, lost 2.
Afterccare, to leave the moss or not? Thats the question. Leaving moss after potting makes it hard to correctly water. Removing it may damage roots. Species will make a difference, but

I reckon experience is key!