Well it's the blind leading the blind here folks. But I'll tell you what I've read and observed so far ok?
One, chocolate mint does not breed true from seed
. That means that if you plant yours Bestofour I have no idea what you will get. Not that, that is necessarially a bad thing. You might get something even better.
Two, mints will grow in full sun or part shade but may taste better if grown where some shade is available.
Three, they like lots of water and the soil should be loose. That way as the stems loose their leaves and the little branches grow they can attachment themselves to the soil and the plant can do it's invasive thing.
Since my soil is more like hard pack unless I cultivate it I didn't have any problems with it being invasive last year. it's little rootless couldn't dig into the soil.
I don't believe it dies back so you should have it all year around once it comes up. But I could be wrong. I overwintered mine inside which is why it is so big right now.
After it gets situated in its new area and digs in good if you would like I'll dig some up and send it to you this fall. But you will have to remind me. My memory is not very good.