Re: 4th box, a supercedure cell and a queen ...I got a question...
Most hives will have at least a few queen cups, you shouldn't be alarmed about that. Having said that I do make sure to keep a close eye on those cups throughout the year. If you see larva in them or they start to get drawn out into full fledged cells you've got to start taking action or you'll likely have a swarm or two. That queen looks awesome. If her worker pattern is anything like that drone pattern I wouldn't care what size she is, she's a keeper. I'm not familiar with your area, but if your flow is still going on I'd probably add another box.
I really wish I hadn't picked NUBE as my username. Seemed appropriate at the time.