I'm reluctant to pick a niche and have no capital left beyond the first month. What can I do, and which payment processor should I use if I'm in a country without Stripe?
I don’t know exactly which processor I’d pick for you, but there are several options depending on your location. In Southeast Asia many people use Payoneer. There are also some Middle‑East‑specific platforms. In the EU you have a wide range of alternatives, though Stripe works in most European countries. Ultimately the best choice depends on where you are, but I’d still go with Stripe in the majority of cases—about nine times out of ten.