Rail trails are generally pretty flat, since trains don't like hills. So an 8-speed might be enough. Trikes have their advantages and disadvantages. They have NO learning curve - you can hop on it and go. And they excel at low speeds, like when you're stuck behind a pedestrian for a bit, or even if you have to stop. But the disadvantages are that they will cost more for what you get, they take more energy to propel, and they have three wheel tracks instead of one. So you don't just maneuver around a root, you have to decide which wheel will take the hit.