It would be fine to stick them in the ground now, just don't expect anything to pop up next week. And if you don't plant for a month, you'll be in almost the same place, as plants grow slow in cold soil.
Don't worry about "jumbo" rhizomes too much. It might improve your first year yield, but a good sunny location and a lot of cow poo will help you more.
I've hear cascades are a good one for first year production, so a good plant to start with.
I grew Sterling in western mass last year. I got about 1/2oz my first year. I could have done a lot of thing better, and I'm going to; this year. I tried some things that didn't work all that well, and thought up with new things (that might not work) to try this year.
With gardening you should start off with low expectations, that way you're always exited when you harvest, and never upset when something gets eaten, or dies.