I pull up a chair and book and pint next to the stove, watch it. If it looks like it's rising too much (I target 245°F), I'll stir it down, or if necessary lower the heat a bit, but I try to not stir as much as I can. But you'll probably have to stir it pretty regularly.
#1 is very light, tastes more or less like turbinado sugar does (slighty molassesy depth). #2 is deeper, you start getting caramel/toffee notes. #3 you get lots of caramel, toffee, I start getting licorice, very prominent flavor. #4 is very pungent, burnt sugar, dark fruit, licorice, etc. I haven't tried adding in siginificant quantities (I packed at 8oz by weight per jar), so it's impact on the beer is subtle. I've been using ~5-8% invert or so, where with Belgians I'll use up to 20-25% candi syrup sometimes, so the flavor impact is very prounounced. Westvleteren 12 (if you believe Brew Like a Monk) is literally just Pale and Pils malt and dark invert. To give you an idea.