For 1/4 acre, I wouldn’t bother with T-posts except at the corners and ends. Line posts can easily be poly step-in posts.
Two strands of tape should be plenty for a horse that respects fence.
The most important part of the fence will be a GOOD charger, properly grounded and hooked up. DO NOT skimp on your ground rods - put them in deep, and use a minimum of 2.
If you do not have access to electricity, Parmak, Gallagher and Premier1 all make fantastic solar chargers. I have yet to find a solar Zareba that works well and consistently. They all crap out after a few months, and never pack much of a punch.
I use Premier1 and PowerFields electric mesh for my goats, and I LOVE IT, but I am VERY wary to use it around the horses. It would be super easy for a horse to get a foot caught in the mesh, and freak out when zapped, and get into all kinds of trouble! I recently got a new horse, and actually replaced an electric mesh shared pasture fenceline before I turned her out, because I did not feel I could trust her judgement around the mesh…