Regional Celeb, welcome to the Brethren and to the world of charcoal. It is a great place to be.
When I do low and slow on the OTS, I find that using basic techniques and a simple side banked charcoal process, I need to add charcoal about every 3 to 4 hours. Note that I have the hinged grates and they are a real nice thing to have. For ribs, I load in a lot of briquettes or lump, and can get 5 to 6 hours out of the load which means no added charcoal for a rib cook. I recommend you get the hinged grate and a couple of fore bricks or clay brickes, wrap them in foil, and use them for holding your charcoal in place for side cooking. They add valuable heat mass and make baking coals easier.
There are many other ways to load a kettle that you will see and learn here, all work great, the longest I have gotten without adding coals is about 6 hours, there are a couple of more advanced setups that I can get more, but, that is more than I would get into for starting up. By the way, if you look at my signature, there is a link to my blog, which is all smoking done on a OTS kettle. There will be some useful information there.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."