My thoughts? I don't like chain driven e-bikes. They are more noisy and more prone to break and the motors are more prone to overheat. Why not just put a hub motor on the front of your trike?
I'd go with a hub motor preferably from e-bikekit.com or hightekbikes.com . Put it on the front of the trike. Then put 24v20AH of Thundersky lithium on the back or wherever you put your batteries. You can get 24v of thundersky for $208 plus shipping from elitepowersolutions.com . They'll last a lot longer than SLA and give you way more distance. Just make sure you learn how to use lithium, they are different than SLA. You have to make sure they are balanced when you use them. ...oos, if you go with a hub motor, you'll need 36v, not 24v. So the battery will be $312 plus shipping. Shipping is about $25 if you live in the USA.
If you want a really powerful hub motor, you'll have to do more research. If you want a powerful hub motor, try
http://ebikes.ca