Can I just drop off tags... Is there a drop box and how do I know if they received them

You might be able to just drop them off, but if they aren't expired you should get a receipt for them, which you can provide to your insurance company when you cancel your policy. If you just "dump and run" the state has no idea where the tags are and, if you cancel your insurance, the state will come after you for driving without! And the state of Maryland is very serious about going after people driving without insurance. The line for drop-offs is usually short or nonexistant (after the front desk), and it only takes a few minutes.

Yes