Training a horse to ride?

Alright, so I'm thinking about getting a summer project horse. This will actually be my first horse but I'm certainly not a beginner. I've ridden a lot of green horses and off-the-track horses and had no problems but I've never worked with a literally never-been-ridden horse before (but I've watched my trainer teach non broke horses though). I'm thinking of getting a three year old half friesian horse that hasn't even been saddled yet. He is very cool and calm, not spooky or hot at all. He is a very chill gelding, he is just such a sweetie and I don't think will be very challenging (it's not like he is a hot off-the-track Thoroughbred or a wild Mustang or anything lol). I will have a little bit of help from my trainer but it will mostly be me. I'm not going to train him to do anything fancy, just to be a nice trail horse and companion. I'm just wondering if you think it's a good idea, and if you have any advice for me. I mean I kind of know what I'm doing cause I've watched my trainer do it a million times but I've never done it myself. Plus, I'll have my trainer there if I ever need assistance. I was thinking of using Monty Robert's method of training. Which I think is a very low stress method that works very well. I mean the only way to learn is to try, right?