First of all I would start with the important stuff and ignore some of the details where it is possible to become bogged down. Look at the aeroplane as a whole, how large does it need to be (how much should it carry), how fast, what size of runway (and so what stall speed), visual or instrument flying, how far, what building skills do you have, what materials do you like to build with, what is your budget and so on. These are interlinked questions, it will take a while to find a compromise that answers all the questions to your satisfaction. Have you joined the local EAA chapter? Perhaps there is someone amongst the membership who can help?