You may want to consider being able to mow along the fence line (meaning accessible by tractor) to make it easier for the horses to see the fence -- AND to keep them not as interested (meaning nothing worth trying to eat so why spend much time over here). My wife (the house horse expert) points out that you want gates/post joints should be built to discourage hoof capture. When looking at gates (and especially portable panels) look for the kind with hoops at each end. That helps to guide a hoof away from the junction.
In my area a lot of folks have field fence (the graduated woven wire) versus simple square (rectangular) wire for either keeping the smaller dogs in, or keeping the smaller critters out. A fence may also slow down fox, etc.
Smooth wire for horses, barbed for cattle (both often used as a topper, similar to the pics posted). T posts can be purchased in several colors, and sometimes different grades (buy heavier than lighter). Though green is most popular, make it easy on your horse (which will make it easier on you) and use the orange. Also, the yellow electric fence t post tops (as advised earlier). Horses are simple animals -- they do one thing well: run.
I bought several $3-10 tools for the clips used with t posts. They were all variations that had a hole in the side and/or in the end, some with a joint in them, that you inserted the clip into and wrapped it around the t post. I found the simplest one was the best. ~3-4" long, it has a slightly flattened end with a hole or two in it, and the other end of the cylinder (1/4-3/8" diameter) is hollow. This works wonders for installing t post clips, especially on field fence (stranded wire has a lot of room around it for twisting the clip around it, woven/fabric fence has lots going on around it).
As in t post, buy the heavier grade fence wire. You will not regret not having to go out and stretch it as often. Also, I happened across a little wire stretcher the grips one strand of wire at a time. Works great when used with a cheap (old deer hunting) block and tackle. Using your tractor is faster of course.
You have an ASV, I believe that is a skid steer? I would visit the local skid steer dealers and see if anyone rents a hydraulic post hole digger and get 'er done. Also, they (Stanley, others) make a hydraulic t post driver. If you can rent one of those, many your pecs will forgive you (watched a fence builder use one, I am sure he thought the ~$1500 was very well spent).
WEAR HEARING PROTECTION when using a post driver. You will be building arm muscles if you are driving them by hand.
Priefert has a new brand of fence called Diamond P that is very impressive.
Diamond P Fence Powder Coated Ranch Rail by Priefert Rodeo & Ranch Equipment
It is wood posts with steel rails that have slip joints in them. Not cheap, but looks very easy (they hog the holes in the posts for angles and made the rails to handle a range of pressure for a curve). Can be ordered in various rail configurations. Talked to them at the Denver Stock Show this January. Would make a great front fence (we are planning on doing this).
