I would sketch out what you want to do first so that you at least get a sense of scale. It's a question of what you are going to use and buy will determine some of these things. At the moment it sounds like you are picking out the new stereo for the car and you don't no what car your getting. This is a sure fire way of wasting money, trust me i have. Create a shopping list of your parts, least you can then decide which ones are affordable and which ones to make. Could save you a lot of headaches ;-)