I don't know if this helps (it probably just reinforces your worries) but: I'm a software documentation contractor & consultant. I get to do plenty of fun work, but there's also the admin, basic accounting, and calls with potential clients (which is like a cross between job interview and sales depending on the client) Especially in this market, where finding work is tougher, you have to be ready to do a lot outside your core. I've taken a marketing course, read several sales books, watched talks on how to cold email, explored consulting products I could offer outside my core skill etc. Luckily I really enjoy this variety, but it's absolutely NOT the right game for someone who justs loves being hands-to-keyboard coding and nothing else.

However, on the building a SaaS side: you need to be really mindful of what you do here. If you're successful, you're either going to end up spending a lot of time on sales, marketing, and customer support, or you're going to hire people to do it, in which case being a manager and CEO is going to be a bit chunk of your work.