Congrats on jumping into this adventure! Here are my thoughts on your concerns:

1. If you communicate that you're in the early stages of building an exciting new business and wanting to get feedback from early-access customers, there should be businesses that are OK with you being solo. They will adapt to that risk, and you won't be able to sell to everyone, but it shouldn't exclude you from everyone either. You might just not be talking to the right customers yet.

2. For milestones (and fundraising) you should think about your goals - what are you trying to get out of this? Do you want to build and scale a big team, serve giant amounts of customers, etc. Or do you just want to augment or replace your income? Or something in-between? You can think about this from different angles: team size, revenue, geographic scope, your personal exit or income, etc.

Here are a couple of examples from my journey in case they're helpful:

In my prior business (https://www.bigleaf.net) my first milestone was to get a working product. I didn't feel as though just talking about it would be convincing enough (and it wasn't), but once I could demo an MVP then it really wow'd customers. Along the way I added a milestone to get a technical co-founder since I got burnt out doing it myself. Those 2 major steps took just over a year. The next milestone was getting our first revenue (took just a month or so after the MVP), then milestones just kept being added from there logically based on the strategic path we chose to be on at that moment.

In my current business (https://www.companycraft.ai) I had a mix of some early milestones. I wanted to talk to potential customers (entrepreneurs) to ensure the problems I wanted to solve matched up with pain they had, and I also wanted to build an MVP ASAP. I completed those in about 3 months, with many other smaller steps and goals along the way. My current milestone is to do a full "v1" public launch in November.

So you just set some milestones that are logical based on where you are and where you want to be in the coming months and years, then hold yourself accountable to them (or ideally be connected with a peer or mentor who can be an accountability partner of sorts).

3. On location, I go back to your team goals. If you're going to stay solo then no, location shouldn't matter. If you want to build a fully remote team then it shouldn't matter much (though being near-ish to a decent airport would be valuable for visiting the team and customers). If you want any local team members then you should think about where you'll gather and what the talent pool is like in your area.

4. It sounds like you're already on a good track here - talking to people who have the pain you're solving and gathering their emails. If that has you on the right track I'd just keep doing that. However you mentioned below that you're selling this B2B...so in that case you may want to consider if you're actually talking to the buyer of your product. Are the people you've met the people who would approve the purchase of your solution? If not, try to connect with those people. Identifying a list of them on LinkedIn and cold reaching out could be one method.

5. Fundraising goes back to your goals as an entrepreneur :) If you want to grow this to IPO or a really big exit, have a team of hundreds, and build a market-changing or world-impacting offering, then you probably need to raise outside funds at some point. However, if your desired scale is smaller and/or you see a path to profitability without fundraising then you get to keep control of your destiny, which is great. If you can afford it and you don't sense the market is going to run away without you, I'd advise continue building, talking to customers, and close your first deals; don't rush into raising money. If/when you know that you can't succeed at your goals without raising money, then dive into that path.