I have to agree with Bale's comments above about allowing plenty of budget for tooling and materials. Tooling doesn't have to be expensive if you get it from places like banggood.com or ebay. Also try to buy tooling wisely, that is only buy what you need and select the most versatile tools.
Small quantities of steel, brass or aluminium stock can be very expensive when postage is factored in, so look for bundles of offcuts from engineering firms on ebay. I'm always on the lookout for metal things that can be repurposed in charity shops, car boot sales etc.