It's growing fast!
The only thing I would suggest at this point is to try not to lose anymore interior growth. It looks like you cleaned out not only the brown needles but also all of the remaining short green needles and maybe even some of the small green shoots and side branches that had started. It's very difficult to get backbudding on a pine if there are no green needles remaining in the area. On a young pine like yours, I've seen it happen on bare wood without a green needle present to produce the new growth, but usually once you lose that interior green, you can't get it back without grafting. If all the green needles are only on the tips of really long branches, it gives a tree a weird pompom topiary look that doesn't appear natural.
Think about how tall you want your bonsai to eventually be, and how thick you want the trunk. Then plan accordingly. Pine bonsai look very ugly before they looks beautiful. That's because very specific techniques are used to manipulate their growth. Here you can see how professional bonsai nurseries do it:
You want to keep your lower branches tight in near the trunk and full of green growth. Otherwise by the time your trunk is nice and thick, all the low branches you want to keep will be too long and out of proportion to mimic a tiny tree. Also check out this video. It's about junipers, but the design concept of keeping short branches is the same across all evergreen bonsai, including pines. With pines it's even more important since back budding is harder to get.
Hope that helps.
The only thing I would suggest at this point is to try not to lose anymore interior growth. It looks like you cleaned out not only the brown needles but also all of the remaining short green needles and maybe even some of the small green shoots and side branches that had started. It's very difficult to get backbudding on a pine if there are no green needles remaining in the area. On a young pine like yours, I've seen it happen on bare wood without a green needle present to produce the new growth, but usually once you lose that interior green, you can't get it back without grafting. If all the green needles are only on the tips of really long branches, it gives a tree a weird pompom topiary look that doesn't appear natural.
Think about how tall you want your bonsai to eventually be, and how thick you want the trunk. Then plan accordingly. Pine bonsai look very ugly before they looks beautiful. That's because very specific techniques are used to manipulate their growth. Here you can see how professional bonsai nurseries do it:
Visit to Telperion Farms - Bonsai Tonight
Plants love Oregon - 100 wholesale nurseries can't be wrong. Many of these nurseries focus on conifers - and at least one grows bonsai exclusively: Telperion
bonsaitonight.com
You want to keep your lower branches tight in near the trunk and full of green growth. Otherwise by the time your trunk is nice and thick, all the low branches you want to keep will be too long and out of proportion to mimic a tiny tree. Also check out this video. It's about junipers, but the design concept of keeping short branches is the same across all evergreen bonsai, including pines. With pines it's even more important since back budding is harder to get.
Hope that helps.