This is what I do at the moment(for a personal project, but it could easily adapt to an early-stage startup): Maintain a task list for the product/business - "action items" that can be taken care of each day. Pull a grab bag out each day and resolve to complete them. So when you want to work on the product itself, you come up with technical tasks, research tasks, maintenance tasks, etc. Or when you want to seek funding, advice, or partners, you create tasks for those. Create scheduling milestones as well. You want to keep moving forward, making decisions, while retaining a balance. Having the schedule helps you to say with confidence, "this is good enough for now," "I can wait on this until later," or "this is critical and has to be done to hit my goals."
It's the decision-making that moves the business forward - as you get used to that, the process of doing the work itself, meeting people, research, etc. will quickly become background elements of what actually happened that day. If you can't make a decision yet, then you need to gather more information. You're either doing one or the other.
An example list of tasks from your starting position would be:
-Research implementation strategies(self-built, outsourced, with co-founder)
-Evaluate early customer needs(example: are you selling a bells-and-whistles "experience," or will no-frills functionality be sufficient to solve customer problems?) and pick a core focus for product development.
-Plan style of external communications - which audiences will be addressed, how to maintain the best relationships over time
-Plan internal organizational structure over some time frame(how big, how quickly, what kind of culture, when do you exit)
-Establish motivations of all potential co-founders vs. self, and identify possible conflict points so they can be addressed early.
