^ these guys are all pretty smart and offering good advice. To me the key factors will be the size of your firebox and your wood, specifically how dry it is. My firebox is 24x24x22 and I use kiln dried hickory almost exclusively so once I get s good coal bed I can get away with a pretty good sized or what I call a full split. Think of an 18" long 6-8 inch diameter log, quartered - that's a full split. I preheat mine and add 1 or 2 every hour to hour-and-a-half depending on how hot I'm running my pit, how crowded it is, weather and a bunch of other factors. One hint I don't think I saw mentioned: you are trying to cook with thin blue (almost invisible) smoke but when you add wood to the fire you will probably get some white nasty stuff. As soon as the new wood ignites the TBS should return pretty quickly; if it takes more than 5 minutes give it some more air and try smaller splits. So instead of a 4 inch wedge, split it down into 2 or 3 smaller pieces. More surface area means they will ignite and get back to TBS quicker. Just my $0.02.
Weber 26.75 OTG w/CI grates & SJ/WSM Mini
Home built 24"x72" reverse flow stick burner trailer with 18"x44" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.