You may have a couple things going on. Or it may all be caused by the valve stem seals. Smoke for a minute at start-up is almost always caused by valve seals. AS the car sits overnight, the oil in the head will pool in the lowest position (valves) and seep into the combustion chamber. When you first start the car, it burns off the oil that has seeped in. Also during deceleration (engine braking) the vacuum created is increased, and sucks oil in through dried out valve stem seals. This is a pretty common problem, and while it may be inconvenient, it's not really going to hurt anything short term. long term you'll be looking at a cat converter, maybe fouled out plugs but it's not going to do any major damage. I'd bet your valve stem seals are pretty bad from the sounds of it.
It is possible that you've got a problem with the rings, but my experience would put my money on valve seals if I were a betting man. But to be safe, I would Check compression, you can "rent" a compression tester from autozone for free.
If compression is good, the engine has a lot of life left in it and it's probably just the oil control rings sticking, causing the smoking. This isn't uncommon to have great compression and smoke. There's 2 sets of rings on the car...
-oil control rings - these distribute oil to the piston and cylinder wall
-compression rings - these are what give the cylinder compression and allow the combustion process to occur.
If compression is low, then compression rings and/or cylinder wall likely has significant wear and scoring. Best bet would be to rebuild the motor or replace it. Probably not much life left to it (I wouldn't take any long trips).
If compression is good, then it's probably either valve seals, or the oil control rings stuck and probably sludged up. Using Diesel, ATF, or a wide variety of other detergents mixed with the oil pre-oil change is something that's been tossed around for a while. Really, the only TRUE way to de-sludge an engine is to take it apart and clean everything, replace what's worn, and put it all back together. However, it wouldn't hurt to put a quart of ATF or whatever detergent in the oil, let it idle for 30 minutes and change the oil. Maybe get a few gallons of cheap oil and repeat the process a couple times. AFter 30 min of idling it will likely come out black as night like you hadn't changed the oil in years. Keep doing this until after the 30 min it comes out looking clean, then put your good oil in and run it. (I wouldn't change your oil filter until you're ready to put in the good oil at the end)
Also just to note, depending on how much your motor smokes it may continue to do so for a while until it burns off the caked oil out of the exhaust pipe.