How do you decide whether to commit to a project?

I have several startup ideas waiting in a drawer, some of which are probably worth further exploring and continuing to a full business plan and start execution. A different person would probably label themselves as a serial entrepreneur that would realize these ideas.

I would like to ask a specific question to those serial entrepreneurs :

1. How do you know something is mature and could work? Do you just start something when you're not 100% sure it will succeed?
2. How do you plan finances of such projects to avoid too much money risk in case it doesn't succeed (for whatever reason)?
3. If you have enough money to start the business, is it wise to approach VCs or just try to break or make it even though ou know you lack some knowledge others may have?
4. What benefits have you had with VCs bootstrapping your startup? Did you get complementary skills that helped you succeed?

1. Pretend you are done coding/developing the product. Try to sell it to real people. Do they bite? No? Great, you just saved yourself 6 months of effort.
2. See 1.
3. VCs will not invest in an idea. You should take your project as far as you can by yourself first. First customers is when a VC may consider listening (unless you have a track record and have already founded a successful startup, but then you wouldn't be asking those questions)
4. Average VCs bring you capital. That's already 90% of the value right there. The exceptional VCs bring you connections and challenge you to be your best.