Just do like I do and knock it out of the park on the first shot!! Just kidding, just take your time. I always sketch what I want in the best detail I can. This really helps me narrow down on critical dimensions and the over all look I want. Also, use some of you stock baits for measurements on stuff you aren't sure about. Maybe a diameter of a body, or a thickness of a tail. My last tip would be turn your shading all the way up and make a print of just the bait in a 1:1 scale. It really gives you a good look at what you are going to get. I put every orthagraphic view and some isometric too. Make sure to make it 3d realistic, and print it out. Look measure, look measure make some changes and do it again.
With your knowledge of venting and injections molds you shouldn't have to worry about the mold its self going wrong. Good luck with the project. I've down a handfull of molds for myself and it is really really awesome to design and catch fish on something you made. Even better than stock molds. Plus it makes you unique. It can be a chunk of change up front, but if you love the bait, whats 2 3 4 grand to catch a couple more bass. RIGHT? Just kidding again.
Oh and like Mr. Junky said, use the 3D printer if you got one. I don't but man do I want one.