For eventing, you want:
Tenacious Trainer
Longevity - sometimes your horse doesn't age. It's like 4 free events.

Fit and Fearless - makes endy cap higher, and since you can redletter that, it's useful.
Grace and Glory - makes sf/movement cap higher.
Then you'll want to add whatever bonus corresponds to the breed type you're doing. So... for training and eventing gaited horses, you'll need Gallantly Gaited. Sport horses, Sporty Sports. It's the +random stat bonus.
For rolling, you'll probably want a second account, and this one can be a novice for sure. All you really need is rolling rodeo, but tenacious trainer + longevity is useful too because you can roll more in less time. You CAN roll on the same account as you do training eventing, but it's sort of irritating when you're rolling a horse that has the +random stat bonus. (So I don't roll gaited horses on accounts with tenacious trainer + gallantly gaited, for example.)
Make sense? I have not had coffee yet. xD