200 amp panel is full, I need to add more equipment. When do I reach a point where I need to increase the size of the panel?

A lot depends on what load you are currently running and what you want to add. If you are loaded with high amperage breakers already, you should consider a higher amperage box. If, on the other hand, you are running a lot of 15 and 20 amp breakers, and plan on using similar loads, you can probably get by, swapping out the 1" breakers and installing 1/2 " breakers or installing a sub panel. You need to do a load determination to be safe. NEC 220 is where you need to go or get a qualified electrician to help you.

Just because a panel is full doesn't mean you can not add more receptacles. You have to determine the draw on your current circuits and then also consider would you ever run say a welder at the very same time you would be running some other equipment on the same circuit. In an extreme example you could put 20 electric arc welders on the same circuit to the same breaker, YOU JUST COULD NOT USE THEM ALL AT ONCE. I have yo agree with ma0641 about getting or doing a load determination by an electrician.