Hi and welcome to the forum!
Well you will have alot of fun! As for exercises to help get ready, you can stand on the bottem stair of your staircase with your foot on it only to the ball, as you would in the sturrip of a saddle. Stand up on your toes and reach for the sky and then drop your heels as low as they can go, this will help stretch your calfs and get a better heels down position. Also, do ab crunches, or any other ab workout. This will help ALOT when in the saddle. As for gear, you sound pretty serious so you will need-
A pair of breeches(AKA Jodphors, Jods, tights) I would recomend the brand of Karrits or Devon Aires, they last FOREVER!
Paddock Boots, I would recomend Ariats, they can be pricy, but will last for YEARS!
A helmet that is cirtified. I like the Troxel brand, they are fairly priced, and are comfy!
I also use gloves, they really help when gripping the reins! I use SSGs.
Also, wear a tightish shirt, because your trainer will want to see your back. I wear alot of polos, because the coller helps protect the neck.
Oh, and, you will fall off! Expect it! I still fall! I fell in the mud the other day after jumping an oxer! lol!
Do you have a Youtube account? I'm StormValleyStables, if you want to be friends!