Hi Maxnchej,
I too just started up a new bl2840 a few weeks ago and am learning the ins and outs of burning wood. A couple of things from another newbie's perspective. As uponthehill stated, beware of opening the door just after the fan has stopped running as this is when flashback has most potential. I'm lucky I kept my eyebrows the first time it happened to me. When I opened the door and the fresh air rushed in, I got a 5-6' flame ball that erupted out in an upward fashion (follows heated gases as they escape out the front door). Now the only way I know if a burn cycle has just happened is to check the temp gauge. if temp is as set point, then I know there's a good chance that one was recent and I approach with caution, opening door slowly and standing to left, behind it. I've noticed this happens more if there's more wood in the stove, holding heat after a cycle. As far as a cap on my stack, I did put one on mine. I just didn't want to have rain water running down my stack. Here in Ohio, we have rain more often than snow. The only down fall to this is that the back of my stove looks a bit unsightly as drops of condensation drip from the cap onto the back of my stove (hey, atleast the stove is black).
I too notice condensation in my ash pan occasionally and the creosote buildup is more than I expect, however, like you the temps here have not been cold and I think with more firing when the temps drop, this will improve.
Hope this helps