As a German having gone through the experience, I feel I am reasonably qualified to give a perspective: The US setup is a breeze administratively, but fairly costly. You definitely need a tax accountant onshore ($3-5k per year at least, more if the setup is more complex) but that will take care of a good share of the minutiae. You probably also eventually need somebody helping you in Germany to take care of employment, taxes, VAT, etc. even though that may not yet be the case. When I've done it a few years ago I found it easier to have a German subsidiary of the C Corp doing that eventually.

If you want a more nearshore solution you may want to contemplate the Netherlands or Ireland which both have fairly well developed support systems in case you ever need help.

The problem with taxes and capital and incorporation is that usually fixing it beforehand is easy while after you start to make money, you are perhaps too late. We went for London because not as litigious, light on paperwork, cheap to incorporate and there is a lot of money slushing around. Not America sized investments but close enough. And easy ramp to the US if you wish. Taxes are quite high once money starts poring in but it is startup and investor friendly pre money.

London probably has most generous tax incentives for startups to offer their investors. S/EIS.

Why not Estonia? Their digital e-residency stuff sounds great and their laws (including tax laws) seem pretty business friendly.