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.