I got into recumbents because I saw one on Craigslist in my area, had never ridden one before, and thought it looked like a neat bike. What I like about recumbents is that the crank out front means there's no one correct way to design one. Each decision is a tradeoff. Want to drive the rear wheel? The chain is going to be long and has to be routed around the rider. Or maybe you have two chains like my folding recumbent and the jackdrive between the two is used to step up the gearing and make a larger effective front chain ring. Want to drive the front wheel? How do you plan on handling the steering? Should the chain twist with the fork? If so, how do you route it without losing too much power to the idlers? Should the bottom bracket move with the fork instead? Should the fork be the entire front half of the bicycle like a python? Should the steering be above or below seat? Direct or via linkage or wires? Should the rider's center of mass be below, in line, or above the hubs? What should the bottom bracket position be relative to the seat? All the options I've listed have been tried and they have their benefits and drawbacks. It's fun to geek out about.