Yes, it is just a matter of adding more when you notice the temp going down. I find I get about 3 hours out of "one batch". You want to use a combination of hardwood briquettes and lump charcoal. Whatever wood you use just use it in the beginning as too much wood isn't so tasty! And "one batch" for me is two chimney's worth of a combo of briquettes and lump charcoal.
It's just a matter of doing it the first time. You'll be able to tell your ribs are done when the meat has pulled away from the ends of the bones maybe about an inch or so. 4 hours give or take.
My biggest suggestion is "just do it". It's easier than you think.
With the residual heat I usually add some sliced ciabatta or other bread - let that "smoke" for about an hour (or add a few slices around whatever it is you are smoking) - or I will add some tomatoes and make some smoked salsa. If the tomatoes end up too smoky tasting you can mix with non smoked tomatoes...or like the bread...add these to the free spots.
With the bread slices I then add a slice of havarti and stick on the grill with the lid closed (indirect heat or a cooler spot). This doesn't take long and is fabulous!