I have a Horizon offset. What I found to be most helpful for temperature control was to have a quite small but hot-burning fire. The splits I was using needed to be split again, lengthwise. These much-smaller diameter splits were placed on top of the firebox before being placed on the fire, so as to warm them to a sufficiently high temperature that they would immediately begin to flame when placed on the coals. This also ended any problem of producing too much of the unwanted heavy, white billowing smoke.
I will place a new split in the fire every 30-60 minutes and never need to adjust any vents for the duration of the cook. The smokestack vent is kept wide-open and the firebox intake vent is held to about 1/2 open....after the fire is well established.
Having come to the offset type of smoker from the BGE ceramics, I was astounded by how much fuel these beasts eat but that is all part of the fun for me, poking and prodding a split or two, every so often, and we really don't worry about a few temperature swings here and there.
Good luck with your new toy!