London could work depending on your business. Hope you involved an international tax lawyer; there can be a lot of issues with the German taxes in this setup if you did not do this carefully.
London probably won't work for me. I have not pulled the trigger yet, tbh I am less worried about German taxes than I am running a C Corp from outside the US. Mainly because of the litigation heavy US culture, opaque paperwork overhead etc.
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.
Netherlands is good as it’s not too expensive (we dropped the 9k ltd thing you also have for gbmh quite a while ago) but the rules and taxes and lack of investors is quite hard; similar things to Germany. You would be bound to those anyway though if your employees are not freelancers and are in those countries…
I am actually not sure if the investor assessment still stands after Covid forced just about any startup to be remote-work-heavy. I don't think most investors care anymore where companies are based or incorporated as long as it is within reason (don't incorporate in Australia unless you are an Australian company) and has a solid and well supported legal system.
The issue in Europe from an investor perspective is that scaling is tougher than in the US. You have to most likely make changes to your product to cover a sufficient number of European countries due to a combination language, currency, regulation, customs, etc.. Your sales and marketing materials needs to at least be in different languages. Your German sales rep needs to speak German and most likely be German, your French sales rep needs to speak French and be French, etc. Add to that the fact that in B2B European companies tend to be less open to innovation. Also, you may encounter workers-councils at your potential clients discouraging changes to processes, etc.
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.
I'll have a look again, got any useful links? I need to relocate to south EU anyway to build my thing, so I am not specifically tied to incorporating in Germany beyond being a citizen.
I have the e-residence, however from what I understand I still need to pay a local resident to act on my behalf for all company matters. Probably OK for a bootstrapped SaaS but I need to raise significant capital and want to make that process as streamlined as possible.