Question re: Oatmeal & Russian Imperial Stout

Hello. Just brewed my 2nd & 3rd batches w/ MRB today; Oatmeal Stout and a Russian Imperial Stout. Added to both 1/2 cup light brown sugar. The Russian Imperial steeped w/ 1 cup coarsely ground espresso.

I've noticed other posts mention that stouts and more complex recipes should remain in a carboy for extra time before bottling. Question is: given that it's not recommended to ferment in MRB beyond 3 weeks, should I buy a couple of carboys, transfer from MRB, and allow these recipes to sit for a while? How long? Also, would I need to collect any of the trub from MRB and transfer to the carboy?

Thanks in advance for the advice. My first attempt, Octoberfest, should be finished conditioning in about two weeks, can't wait to see how it turns out.

I usually pull my beer off the yeast from between 2 and 3 weeks... transfer to a secondary (or keg) and age as needed