I went to my bonsai nursery and picked up five bald cypresses and they were all in a pot together. I wired one and there weren’t that many branches on the back and near the base of the tree. I tried my best. This is also just its first styling and the rest of the trees are not wired yet. Any advice?

I also think the rest of the trees will help with the bare back of this tree.

Can't se all of it, but it seems quite tall, you can let a sacrfice branch grow on top so you can thicken it, bald cypress has an awesome texture to the trunk when they ge thicker...

I don't have that species but I know they go well on Forest style, but maybe you want to separate them and grow them a bit individually before putting the forest together...

(Sure, it must be all done on the proper time of year...)

So should I just bring an existing branch up and make it the new trunk. If so how would I do that and when. Thank you

I think you should do some research about sacrifice branches...
Is a branch that you let it grow unprunned in order to thicken it.

I'll give you an example, look at this cryptomeria, you'll notice that the tree structure is all on the lowest part of it, and the top of it still going, once the desired diameter is reached, that segment is removed...

How would I do that because there are no branches on the bottom of the bald cypress.

Well, if i think a plant is too leggy, I would avoid buying it on first place...
I mean that's a very common issue when you buy plants from gardens that were never meant to be trained as a Bonsai, that's why choosing material is a very important thing.

However that doesn't mean it can't be done, just that it will be harder...

I think Taxodium can be hard prunned or air layered, you can start by doing some research on that.

So can I air layer at the bottom of the tree and cut the bottom off and shorten the tree when the air layer grows roots?

Like I said, do some research on air layering, so you can understand what I'm talking about.
You'll basically divide your tree into two, that's not quite a begginer technique, but I don't see many options, is that, or to hard prune it low and start the branching all over... Just have in mind that this is not something you should do right away...

Ok