1) You can continue the 4" all the way to the laundry if you wish. That may allow you to have a 4" end of the line clean out. You should have a clean out under the sink also. If the whirlpool vent is within 5' of the 4" line then you won't need a clean out on the 2" whirpool drain. 2) Yes, the 2" venting works as long as they are tied together at least 6" above the sink. 3) The whirpool vent looks ok. However the toilet vent should come off of the toilet branch not off the main drain line. You can vent up the wall between the toilet and furnace. 4) Does the shower have it's own vent?