Thank you minorhero! I live between Hyattstown, Clarksburg and Boyds. Your tank plan sounds really cool!
For catching darters and minnows, I'd love to use hand held dip nets, but, unfortunately, you aren't allowed to use them for the species that I'm after, including darters. Maryland has some funny laws regarding that, but it's to protect species that are endangered and/or gamefish, so, I understand. The best way to catch them legally is to use a seine and kick them into the net. Two people working it makes it much easier, but, here's a video showing how to collect fish using a small seine with one person: https://www.youtube.com/watch?v=VCVaXSXWNlY
Here is the law for using seines in nontidal waters:
(5) Seines in nontidal waters:
(a) Shall have mesh no greater than 1/4 inch;
(b) May not exceed 6 feet in width and 4 feet in height;
(c) Shall only be used to catch minnows and other bait fish;
(d) May not be used within 50 yards of the base of any dam or the mouth of any river or tributary; and
(e) Shall only be emptied from shore.
Let me know if you are interested in getting a seine like this and I can find the manufacturer that I got mine from. I can't remember off the top of my head.
As far as locations to catch any species in Maryland, this is a great site: https://geodata.md.gov/streamhealth/