I work probably more than this and the balance is hard, but I found that it helped to have boundaries. If you give all your energy to your day job, you don't have much left to give.
I would do the youtube on the side, it will take time to build up anyway and will give you the motivation and energy to use your creativity on something fulfilling.
If you can make more in your day job, it's never a bad thing, as long as it doesnt drain you to a point you have nothing left to give on your passions.
This is where some up front validation is handy. You have an assumption that slack is what everyone would want, but do you have any data on this?
Would other integrations be beneficial?
What's the feedback you're getting when speaking to companies about this?
Is this a problem that people are trying to solve?
It looks like it could be useful in your future plans, but really honing your value proposition as to what problem you're solving for the startups would help on your marketing I think.