Nice tank, as for clean up crew I would add 2 -4 turbo snails, a couple of red leg hermits or one blue leg, a shrimp either a peppermint one or cleaner shrimp. That should get you started as you van always add more when and if you want.
You say the tanks been up and running for 3 weeks that's not a lot of time to be honest, I would wait for a month poss more and keep testing your water to see if it has cycled fully.
The most important advice I ever had in this hobby was to take it slow and go with the flow. Hope this helps.