You can use this link as a guide http://www.wyntk.us/food/smoking-tim...eratures.shtml
but just remember that as mulepackin said, it all depends.
With your corned beef check the sodium level, most likely you will have to soak it in water for at least 6 hours, but not always. Would depend on your sodium level.
At the very least I would rub the corned beef with some black pepper and coriander or juniper berries, roughly ground. Maybe a touch of garlic, the recipes are vast.
Seasoning that day is perfectly fine, I always rub mine down a few hours before smoking.
Some may argue that smoking a corned beef makes it pastrami, some argue that you MUST season it to make pastrami, honestly I couldn't tell you if there is a definitive answer but it will be delicious.
Just smoked up a bunch of corned beef recently and tried them 3 different ways for texture/taste testing purposes. Maybe this will help out.http://www.smokingmeatforums.com/for...light=pastrami