I've had some problems with a sticking clutch as well, and I found that the best remedy was to disassemble it completely and clean and de-grease every part. In our clutch (and I mean the clutch itself) nothing should be lubricated, it's designed to do without. Grease will only attract dust, which will make it stick again soon...
On the other hand, the torquedrive (the moving driveface behind the clutch plate) and bearings (inside the driven pulley) really do need lubrication ! Once you've removed the clutch plate you can easily take apart the rest of the driven pulley assembly, and you will see what I mean...
Be sure to use a good quality high temp mineral based bearing grease (no silicones here !)... Take it easy on the amount of grease, since an excess of it will be pushed out onto your belt and clutch... It's safer to use less grease and check this more often (every 1000 miles or so at first) until you get a feel for how much is needed and how long it will last...
Regarding your choke problems : first make sure your carb is setup right, the automatic choke should work fine when jetting and idle mixture are right. If you're really not getting up to speed after some warm up time, your engine is probably just running lean, fix that first - the choke mostly works in the idle range anyway...
+1 for tortoise's choke switch idea by the way... The standard choke is fine, but in very cold weather it shuts down a little too early sometimes.. Switching off the power to the choke for a while is a very nice and clean way to delay this ! (I still have a thermostat switch laying around somewhere that I wanted to try for this purpose, maybe a nice experiment for this winter