This is my typical set up for ribs.
I do what I like to call the corner burn. I'll fill up up one basket with coals and what ever wood chucks you like, except leave one corner empty. Lite up about 10 or so coals and dump them that open corner, it'll burn like a mini menion method.
I never count the number of lit coals, and if some spill over to the sides, that's okay. This will get the kettle up to temp pretty fast, so once it starts approaching desired temp (275-300 is okay by me) I shut the bottoms vents to almost completely closed. If you want lower temps, just start with fewer lit coals, it'll just take a little longer to come up to temp.
This will hold temp for plenty of time to cook a rack of ribs and I've never had to refill or add coals. In fact the first time I did it I think I added more coals just to be safe but it turned out I didn't need to, and never have since.
Here's some ribs about mid to end cook, you can kinda tell there is plenty of coals left, and see where some had spilt over the edge when I dumped them.
I love the way the ribs come out like this. I don't wrap them, but I do like to mop them with a vinegar sauce after the bark is set.