Take an Executive Assistant role to learn about operating a company?

Why are you so concerned about -- possibly imaginary -- social pressure?

Take the job and you'll discover quickly enough if you're learning valuable skills. No need to overthink this. Startups are always looking for talent, so when they discover they can trust you with bigger responsibilities the odds are pretty good you'll move up quickly.

Leave if they force you to do menial work every day. Easy as that.

You probably won't learn as much as you think this way.

However, you will make some valuable connections. But you'd also make those connections in a more substantial role. I'm guessing though, that you aren't qualified for that though based on this post.

If all your light bulbs are on, you will learn a lot from an EA role. You would learn equal as much from a sales role. Choice is up to you.

Ok, here's the deal (and I've done this). For making relatively easy money while building a business, you can hardly beat an EA or AA position. It isn't "mind intensive" which is crucial when you know you're spending your off hours at home building you own business. Also, depending on what company you work for, everything goes through your fingers so you really are in a great position to learn a lot of valuable info that you can use in your own business, and see in real life if it's of use or not. Depending on your resume it will be hard to get such a position. For instance, in interviews I was frequently questioned as to why I was taking such a position when I'd been a Business Analyst and was paid much more in previous positions. If you can answer those questions creatively and get your foot in the door, go for it. Use that income to build your side biz until that side biz becomes your only biz! Good luck!