Work Load

I have lots of thoughts about starting my business. Many of them are around the idea that I will need to invest SO much time to get it going and I don’t know if that’s possible to do with only wanting to work less than part time.

How do we figure out how much time we will need to build our business?
How do I overcome being completely stuck in inaction when I don’t want to get in over my head by taking on too much?
I know a middle ground exists but I can’t find it.