It looks like you have some good starting material. The trunk is skinny for my taste and the taper of the trunk is minimal. On the good side you have a lot of lower branches and that will help you thicken it up. Doing this along with letting it grow will help thicken the trunk. Without seeing the larch in person you are probably 5-10 years from it being a good bonsai. It has a fast growth rate which is nice.
I would suggest this journal post from Nick Lenz about Larch. If you google Nick Lenz include bonsai in the search because there is another one that did some bad stuff. Also Nick is very big into the "Art of Bonsai" type of work.
bonsaijournal.com/larch-with-taper.php
If it was me, I would plant it in the ground (or if that is not possible, a slightly larger planter), Cut it back and create a new lead, and fertilize it.
My favorite B.Empire post about working the trunk.
www.bonsaiempire.com/blog/bonsai-trunk-creation