Sounds like you already realise that this tree is very tall and skinny so lacks impressiveness (is that a real word

)
Ben has given one option to reduce height and give more drama to the trunk - wire and bend.
Pruning is another option which will improve taper as well as reducing height. Note that shorter trunks actually look thicker than tall ones even if there is no actual difference in diameter.
The thick branch near the top is still a long way up. It also goes toward the current back. Apex looks far better when it comes toward the front of the tree so unless you can wire the trunk and bend that branch forward a bit or change the viewing angle (front) it is probably not a good candidate for apex - Look lower for better candidates. The best tree is probably in the first 3 or 4 branches. I know that's a lot to cut off but sometimes going backward is the best way to go forward. Looks like there are plenty of options for differently styled bonsai in those lower branches. Another alternative would b to remove some of the lower branches and create a tall, thin, elegant bonsai with minimal foliage and branching - sort of literati. giving lots of alternatives is probably not helping your decision making processes though
re pruning junipers: They can shoot on bare wood but it is not a good idea to let them grow too much. Regular pinching is probably best maintenance most of the time. Older wood cannot be hurried. The shoots will mature and thicken in their own time. Need to be patient with bonsai.
Funny branch could be used for either sacrifice or jin. I'd usually vote for sacrifice branch because growth is normally quite slow. sacrifice branch will help with some thickening. The trouble with converting branches to jin is that the bark makes up quite a lot of smaller branches. I think if you make this into jin now it will be very thin and threadlike rather than impressive old, dead branch. allowing it to grow freely as a sacrifice branch will allow it to thicken and any jin will be better after. trouble with sacrifice branches is that the tree will not be 'bonsai' while you have sacrifice branches. Are you patient enough to wait for a few years or even longer?
Hope you get some good ideas.