Fencing Type

So you're keeping the barbed wire and adding some electrical to keep the horses off of it? The cheapest easiest would be electric rope or tape, imo. You have to be sure to keep weeds off of it, though or it will ground out. I had solar and that worked pretty well.

You will probably use existing poles but you can actually space this stuff out on poles nearly 35' apart. No corner bracing needed (but I used posts on the corners and t-posts down the line)

I was under the impresion you had to be a certain distance 1-2 ft away from the barbed wire.

I can understand not wanting barbed wire around horses. It's sort of an accident waiting to happen. I had smooth wire which is bad, too. I put electric at the top. Once they get zapped they'll stay away from it. You can use the same posts. If a horse is going to run through a fence, being off it a couple feet  probably won't stop them. Just my opinion.

Oh, you can get some insulators that stand off the post about 6 inches or so...

The person interested  wants the  the electric fence to be 2 - 2 1/2 ft inside of the barbed wire.  Top strand equal or slightly above barbed wire and a second strand 1/2 way  to ground.  So I may end up installing corner posts and some T Rail.  I was thinking on using the bare wire not poly and tying flagging on it.

Instead of any electric fence is it acceptable to run 2 strands of barb less wire 1 at the top and the other half way to the ground?

I personally wouldn't use any barbed wire for a horse fence. If, God forbid, a horse does get tangled in it he'll likely panic and could get seriously injured while trying to escape. Your options, according to cowgirlu.org/what-are-the-safe-horse-fencing-options are pretty much either a wooden fence (which is generally more difficult to install and requires some maintenance), a plastic fence or an electric fence. These are really the only three people use if they want to be safe.

I also don't like barbed wire for the danger it possesses. I also don't like how terrible it looks on photos.