The smoke is the strongest in the first hour or so of the smoke, and then it tapers off to almost nothing that can be noticed. Nevertheless, the smoke is still there, just not visible. With a small pan of apple juice, etc in the bottom of the smoker, you will see I guess steam coming out from the smoker, and perhaps some smoke.
You definitely do not want to add wood after you start the smoker! The smoke box is very hot, and should not be removed until the meat is done. As a general rule, 4oz or so of wood should be sufficient for most smokes...for longer smokes (like boston butts), you might want to increase this to 6oz. If you have a food scale, you can weigh your wood to know how much you are using on any smoke.
As for the belch, that happens when the wood catches fire...for me this happens at around 180F, and then all is well afterwards. A couple of ways to avoid this are to slowly ramp up the temp, or I have found recently that putting the wood in foil and punching small holes in it works to restrict air to the wood, thus avoiding the wood catching on fire.
