Natalie I've used black nursery pots for W/S, I don't see why you couldn't use the coffee containers with plastic on top. I use baggies on top of some of my containers.
If your temps are staying cold during the day it would be okay to start...the containers act like a little greenhouse so if the sun is warm and the container warms up they will germinate. I start some of mine in the next few weeks, but wait a bit for the tender annuals.
What are you going to try?
