I think your idea should work for noise reduction, and as for surface agitation, testing is your best bet. Ideas that I thought would work to prevent stagnation often ended up not working. I made a small "test" sump out of a small rubbermaid tote and used pieces of another rubbermaid tote for baffles. It took me maybe about 6 tries to come up with a design that worked for me. That's the thing about DIY sumps. They require a bit of tinkering, but once you get it right, it feels really good, and it works better than any premade sump that you can buy. Anyways, back on topic, I always wondered what that very first baffle is for. I've seen a lot of people and prefabricated sumps use them, but I never understood why they are used. They don't really force water through a certain path. Water could just flow over the top without going down the baffle. Anyways, that's just me. I'm just curious. Always like to learn new things.