Making a musical 4: The fear sets in

Okay, so now the fear has set in.
The sheer enormity of the scale of what I am trying to achieve has finally hit me, akin to the way the apple hit Newton under that tree so many years ago.
How the devil am I going to pull this off?
I mean, seriously, this is like the hardest thing I've ever conceived of undertaking.

To write a musical is one thing (which is coming along great actually), but then think of the music... the dancing... the acting... the filming... the dedication and time it will take of so many people that I can't afford to pay.

My biggest fear is that I'll push loads of money into this production, and be let down by people who say they're committed, but then flake - which is to be understood. I mean, when you're not getting paid, and someone is taking your time up for like 6 months, it's very easy to turn around and quit.
And that's just it, it's not a short production. It's going to be time consuming -because everyone needs to learn to dance, and the singing needs to be done. And then memorising your lines as well as dances... I mean, imagine how long that will take? 6 months? 8 months?
Who can stay committed for that long, when they're not being paid?

So what do I do?
Does anyone have any words of reassurance for me?
Any film makers out there got any tips?