Great questions.
> What are your ways to find people that have a problem?
Below are some very generic ideas around how to find people. These same ways of finding people are going to help when it comes to actually marketing and selling products, so if you can't figure things out at this stage, it's going to be potentially difficult later down the track.
The key idea is to go through a problem solving process asking questions such as:
Are there places these people hang out? Forums / Facebook Groups / Events / Subreddits etc
What complementary products or services are these people using? Can you partner with them in order to reach your potential future clients?
When people have this problem, what do they do to try to solve it? Are there things they might do that can identify them as potentially having this problem?
When you can answer these questions it should become clear on how you could potentially reach out and get in touch with these people.
> How do you avoid potential burnout?
It pays to probably emphasise "as much time as you can". As you can without going insane, as you can while maintaining your mental and physical health. As you can while being able to survive and pay your bills.
It pays to solve a problem that resonates with you personally so that you will still have drive when times get tough.
Something I've been working on is cutting out as much unnecessary stuff as I can, dropping email subscriptions, dropping commitments to things I don't care so much about. You can tell when you're pushing your limits, you just need to keep an eye on it and manage yourself as is appropriate for you.