I’m a little bit surprised by some of the pessimism here. OP, I’m a h/j rider and I do exactly what you’re trying to do. I think as long as you’re clear with all involved, it is entirely reasonable to expect everyone to play nice.
My trainer connected me with both a dressage trainer and an eventing trainer, and I take monthly dressage lessons and train with the eventing coach at events. I’ve also done a few eventing clinics over the past two years.
I absolutely agree with what people are saying about the differences with reading a cross country element or riding over terrain. But I don’t agree with the extent to which people seem to think the jumping skills don’t translate. There are a lot of h/j riders who ride “forward but defensive” just from the types of horses they ride - greenies, horses with a stop, horses half-broke they’re trying to get around, etc.
Last year I was showing my horse in the 1.0m jumpers and BN eventing, and even with limited access to cross country schooling/instruction between events, we were able to have successful, confident outings at BN by training with my h/j instructor at home and meeting up with my eventing instructor for events. If we decide to move up to novice this year, I do expect to try for more regular cross country schooling for both us. I don’t think anything you’ve said is unreasonable, especially if your horse is naturally brave.