Creosote :(

Your wood stove will run much better and cleaner with a liner. The chimney flue is too big and is condensing as it gets out side. Yes you should keep sweeping it once a month. The amount of creosote that is in your dust pan photo should be for the year. Make sure you do a free burn each day (leave your door slightly open 1/4"-1/2" for 15 minutes to really warm everything up. Good luck keep it up you'll get it clean.

after a full season of burning wood much worse than 25% in an open fireplace (roughly 1.5 cords), my larger flue did not look that bad prior to having a pro sweep it. Conversely, the 6 inch flue where I was burning a mix if 75% kiln dried with the 25% of the aforementioned wood had zero creosote...maybe 3/4 to a 1 cord went through that one. Obviously much different winters from last year to this one, but seems like you're getting more than your fair share of build up. Best to keep sweeping it, start doing top down fires to warm it up a bit or adding splits every few minutes for reload so as not to be cooling your coal bed down all at once, or split your higher moisture wood smaller. Good thing you're keeping an eye on it....better than most folks. There have been two chimney fires in the past two years within three houses of me. We're somewhat secluded and a relatively crime free area so when I see the lights during winter, I instantly assume chimney fire. 2 out of 3 times I've been correct. We also have a lot of elderly living in the area...the third time was an accident with one of them and some stairs. Best of luck on keeping it clean and enjoying the heat it provides you.