In this case, I think you will get excellent results without needing to add much to the 750 mg/week testosterone enanthate base.
A funny thing is that while it might be guessed that steroid dosing is extremely precise, actually dosages are typically based on round numbers of mL! And this works absolutely fine.
So the recommendation here is assuming the trenbolone enanthate is 200 mg/mL. As you're planning 750 mg/week of testosterone enanthate, I'm guessing your product will be 250 mg/mL, and you're planning on injecting 3x/week. If not, then things can be adjusted.
Adding 100 mg of trenbolone enanthate per injection is being pretty modest, yet will give a significant edge and will already move you up to just over a gram per week of injectables. Trenbolone-specific side effects are unlikely to appear at this dosage.
As you're already using a decent amount of testosterone, Dianabol doesn't need to be at the 50 mg/day level that ordinarily I'd prefer, when that's not the case. You could do fine with 30-40 mg/day.
This would put you at about the 1300 mg/week total level, which is quite solid. I think there is no way this would be insufficient or unsatisfactory for you.
If you were not using the Dianabol also, there would be a chance (no guarantee though) of the 750 mg/week testosterone usage not raising problematic issues with estrogen: adding in the Dianabol, that's still possible, but less likely. Letrozole 1 mg/day is a reasonable estimate with this amount of aromatizable steroid (about 1 gram per week), but I'd test estradiol levels two weeks into the program and adjust as necessary. It is easy to order the test online, and not expensive. It's very much worth doing.