Another person looking at doing a PhD in Germany! There are dozens of us! ? I'm not sure if the university you're apply to has a different set up, but since most German universities don't have a structured program, and so the usual set up of PhDs as TAs or lecturers receiving a stipend isn't typical. In theory, you should be able to do all your research and update your supervisor remotely. In order to receive documents, like your log in information for the library and things like that, you may need an address in Germany which the university can send things to. If your intended university has an international office, I would contact them to discuss the logistics of that, which they should be somewhat familiar with because of the pandemic which trapped many students who had intended to relocate to Germany in their home countries.
When it comes to funding packages, because there's not a structured program, most students are responsible for finding their own funding (and sometimes that applies even if they're in a structured program). Your university may or may not be able to cover a travel stipend, but this is worth discussing with the international office. I will always recommend contacting the international office in these cases as many of them are either internationals or are used to understanding the gaps in knowledge which internationals have of the German system and its... quirks. If you're already receiving positive feedback from potential advisors, as far as I know, your advisor essentially "claims" your project proposal in the committee meeting approving PhD candidates, so there's not really a financial concern they're considering, as funding is your responsibility. If you hope to relocate to Germany one day or find funding, your advisor will write letters and help you network, so having a relationship with them in which you feel comfortable discussing the challenges and needs you're facing is important. In German, advisors are jokingly called Doktormutter or Doktorvater, after all.
Sorry for the tome, but good luck and feel free to reach out!