How to evaluate if the support and maintenance work is worth it?

There's a lot of uncertainty in building a SaaS product, but it's one particular type of uncertainty that makes me worry: on top of all the work that you need to build the product, there's going to be lots of maintenance work. And it's hard to evaluate how much work that will be.

So I find myself asking questions about the products that I'm building;

• How much time will it take to support and maintain it?
• How will the support and maintenance work scale with the number of users?
• If I'm scaling, how easily can I hire and train people to help me manage it?

And my biggest question:

• If my product starts to get successful, will it get easier to step back and have more free time for work-life balance, or will it be harder?

I'm giving these questions more thought recently, ever since I had some projects that took much more ongoing maintenance that I thought, and after some experiences that made me realize the importance of good work-life balance.

I'd love to hear from IH: how do you estimate how much support and maintenance your product will take? How do you approach these questions?