You need a producer, or a production manager or whatever you want to name it; a partner who is responsible for the business/logistical side of the production. This person needs to share your vision and your passion, but will be the one who reigns you in when you get too "crazy," to help you maintain your perspective and keep you on budget.
As Lucky said you need the script, but you need to start on the shooting script. This will assist you with deciding the size of your cast and crew, locations and props, etc. and how to disseminate your funds to best effect. BTW, you should hold back 5% to 10% of your available funds for emergencies; you will ALWAYS need it.
A successful shoot is all about preproduction. You are a "general" leading your troops into "battle." "Battles" are won by thorough planning, the most important of which is logistics; organizing and assembling all of the tools and personnel that you need; knowing who should be where, when they should be there, how you get them there in a timely fashion and what they need. Have back-up plans for when things go wrong - and they will.
Treat your people well, always be looking out for their well-being. Happy, motivated people work harder for you.
Preproduction, preproduction, preproduction!!! It's all in the planning.