I would first concern myself with getting it out of the nursery soil and into a bonsai substrate. I've bought many Iseli plants and their soil is mostly composted bark that is probably okay for at least another year. Nevertheless ...
The first thing you may want to do is to wire the branches to simply spread out the foliage. You could do that as soon as you've got the appropriate wire in hand. I urge you to NOT start pruning off branches to 'open it up'.
I suggest doing the famed half bare rooting (HBR) where you will remove the soil from just one side of the trunk, plant it in substrate and then spring 2022 complete the job. If it is growing vigorously after the HBR next spring, you can finish the job earlier, sometime next summer (i.e., between the time of the summer solstice and the autumnal equinox) instead. Of course, the first step after you knock off the plastic pot would be to saw off the bottom third or so of the 'plug'. Meanwhile you should study and scheme. The foliage, especially newly hardened foliage, powers root growth.
Also during the meanwhile, you can do a bit of playing to learn how it responds to candle treatments. You only need to try a treatment on one or two branch tips as what you do to one has little to no effect on the others. There are 4 principle variations, IMHO:
- like a JBP - cut the new terminal candle/bud before or about the time of the summer solstice
- like a Scots - break off part of the candle as it extends and maybe again as needles start to emerge
- like a JWP - cut off only part of the new shoot after it has hardened (probably not long after the summer solstice if not a bit before)
- like a mugo - cut off the entire new shoot once it has hardened
Again, just try these on four branch tips and see. You'll be looking for whether the needle length is reduced, whether a new terminal bud is set and whether back budding occurs as fascicular (or needle) buds being released and/or epicormic buds at points on stems where there no longer are needles (most likely these are at a lower node, but might be on internodal stems). It could take until spring 2022 to really know - damn pines are often slow to tell you what is going on.
This is all a lot of play one day and wait months = frustration, I know. But it is also a lot of time to carefully consider what you're going to make of it. You've got a nice first trunk section coming from the soil. Via the HBR-ing you will know what the nebari looks like. Pick the view with the nicest looking nebari as the front of you composition and ask yourself what you're going to do with the rest of it. How tall a bonsai are you going to make? The rule of thumb is that the height ought to be about 6x the base trunk diameter. The tree becomes a more feminine form the higher this multiple and, as such the trunk ought to sinuously curve along. The classic masculine form is a zig-zag trunk. Shohins are less than 25cm/10inches tall and, as such, would have a bottom trunk section about 4cm/1.5inches or more. Likely you would need to have some serious needle length reduction to make a sensible shohin..
If you are going for a zig-zag trunk, you'll need to find a branch with foliage close to the trunk that will become the next trunk section. Then you would remove most of the other branches, basically only leaving foliage at and near the top of the present trunk. Then it is let the top growth run until the lowest trunk section is as about as thick as you want for your bonsai. Then you'll eliminate that sacrifice and let that branch run that will make the second section of your zig-zag trunk and rinse and repeat until you have your tree. You'll recognize, I'm sure, that you need something to be a branch at the points of each zig and zag.
The alternative is, as I said, a feminine or curvy form. Basically, you would wire the trunk and twist/bend/crunch it into whatever shape you do. It might dip down like a cascade and then rise back up, go over there, and wind around over there. Of course, you could pick a branch and grow it to do this; it doesn't need to be the trunk, per se.
It is all up to you. Personally, I get my kicks bending/twisting, but I'm really pushing myself to make a zig-zag (can't be a one trick pony, should it turn out I even have a trick !).
Oh. I forgot one thing. You probably don't want that trunk to be coming out perpendicular to the soil line. It only works with form uprights which are about the most difficult bonsai style as there is to make.
Nice tree - enjoy the adventure!