Minnow traps are fine, cast nets are fine. You can catch your bait and keep it in a pen.
There are requirements on the trap itself the specs are on the website, but store bought all meet specs. Also last year they started requiring you to have name, address, phone on traps(or floats attached).
Check the DNR website if you want specifics.Also be careful what you catch in your traps, not all are legal to keep. While small flounder and hardheads are great live bait, the man will bust your ass if you get caught with them! Good Luck
I've been using the cylindrical type of minnow traps in Southern Maryland for about 40 years and have come across many DNR folks over the years and no one has ever said a word about having the traps. I think with the square ones you catch more "questionable" bait like small flounder and hardhead.
We use to stretch a fan safety net over a frame and suspend it in the water and would catch minnows like a gill net. I'm not sure where one could find the nets antmore.