The conventional wisdom in the orbit of YC/HN has become acquire the first users one at a time by building something that they love and use. Worry about techniques that scale later.
However, the question seems to contain an ambiguity. Is your project ultimately focused on the needs of businesses or individual users?
My random internet person's advice, forget about sign ups. Forget about pre-launch. Build something basic and launch it to one person. Talk to that person. Launch the next iteration to two people. Iterate and launch to four. Keep going until you know it works or it doesn't.
Good luck.