Auto Throttle

I’m currently working on a high speed high atmosphere fixed wing aircraft, at certain speeds it will begin to tear itself apart so I’m trying to implement an auto throttle system so I can do steady flights without having to bounce between millions of controls (it has lots).

I’d like if someone experienced with Vizzy can explain how I can do a few things, primarily I’d like a system where I can hit an activation group, it prompts me with a select speed, and the auto throttle will bring me up to, and hold that speed until I disable the auto throttle. A secondary system would be throttle dampening as it approaches it’s set speed, right now the program it’s running checks its speed every tenth of a second and will either cut or max out throttles if its over or under a preset speed, very simple, so I’d like something that can smoothen that process out. And third but not really needed is a max throttle prompt as well, because my vehicle is powered by turbo jets as an alternative low speed power source, and rocket engines as a high speed source, I don’t really want the after burner running 24/7. If anyone can give pointers on how to achieve this I’d appreciate it.

Alternative:
When AG3 is activated it grabs current speed and holds to that speed.