Whatever you choose for suspension, if you also want e-assist, I suggest a mid drive like Shimano Steps, which is a torque based system. For me, my 2021 model, limited to 250W, provides a very natural feeling pedaling experience. To be honest, mine was the stock e-assist on my ICE trike, but the experience should transfer to a mtb or gravel bike, depending on what you want. I have a ten speed cassette and I use every one of those gears. In fact, I changed the front chain ring from 44 to 38T, and I changed the cassette from 11-36 to 11-42, and could still use some lower climbing gears sometimes. I strongly recommend against a more powerful hub motor with throttle, unless you want to give up pedaling.