Do some searches on the site, I'm sure you will find information on yeast harvesting.
What you have to worry about is the age (in generations) of this yeast. Knowing this is a new Rogue line, it's probably not that old. Yeast can only be used with decent viability for a few generations. Having never actually cultivated yeast, I wouldn't be able to tell you how to go about this, but being a bit educated on the subject can never hurt.
Try and harvest the yeast just after they peak in reproduction (and fermentation) this will give you the highest cell count. Wait too long and you will have more dead then alive cells.
As for your question regarding stepping up the wort, here's my answer.
The more wort for them to ferment, the more yeast you can cultivate. But be weary because too many fermentation cycles will get your yeast cells older and less viable for re pitching. Which is the entire goal of this right? One liter may be fine, but if you aren't happy with the amount of yeast culture after a 1L ferment, then I would step it up to probably 3L just once. Try to get enough to use for different styles.
You don't need too much malt content, I've heard to shoot for 1.040-1.048 OG for wort used for yeast propagation. Also don't be afraid to hop your propagation wort, hops will not alter the yeast and they can help aid in bacterial protection.
As for storage you will need a medium to store the yeast in. I've believe you can use wort or even beer, but you should confirm this elsewhere, I don't have my handbook with me right now. You should be able to find this information on the site though as I'm positive others are doing this successfully here. Store the close to freezing, so they can go dormant.
Hope this helps and good luck.
Keep us posted
:rockin:
