I think in Maryland, you can request to have to reviewed every 3 years.

1. There is no court requirement to adjust. You could, in theory, set it at one level and if neither party requests an adjustment that would be the same amount until the CS order expires.
2. It depends on what your agreement says. If you have a regular order yes you will have to petition to modify it. You could also have a provision in your agreement to exchange information at the end of every 1/2/3, etc. years and modify using the guidelines in effect at the time. You would need to have a provision in the agreement on how to handle a disagreement on the amount.
3. I don't see how a provision requiring the higher earning spouse to adjust would be practical. You would be better off having an agreement to exchange income information at set intervals.

What is the best online calculator to use in Va?

It depends on how your child support works. Usually you have to go back to court.

My ex and I rerun every January once salary increases and insurance costs adjust. If there’s anything unusual (like when I had a temp promotion for an acting position) we rerun then as well.

We have a very amicable coparenting relationship though, and we just do this ourselves using the online calculator. No courts are involved.

For 50/50 custody where one spouse has variable, but steadily increasing income. Do the courts require an annual adjustment? Does the spouse receiving child support have to request it? Or is it on the higher income spouse to proactive adjust?