It of course will depend on the level, faction (which determines your starting position), and whether you selected a GA or total domination game.

I am currently playing the Italians on expert, GA, and for the first 200 years I didn't take any new territory and simply buiilt up troops and buildings with trade later giving me a good bank account of 100K (I don't know how some people manage to get a million). Now in around 1340, I have a good chunk of Europe and Africa and am one of the 2 largest factions ( the BYZ, Norg are the other 2 main competitors). The Alomonds are gone (wiped out by the Spanish and the French)the French are gone (wiped out by me) and the Spanish are down to one territory. I have been excommed, but of course I eventually expect to see trade come back as the rebels will trade( I didn't take a few provinces), but at the moment I need to jettison my mercs soon, as my war chest is down to 5K plus

So how quick you expand depends on neccessity and your playing style. Sometimes just attacking provinces for plunder and/or ransom, and leaving them to revolt or be re-taken after they have been stripped is a fun strategy. I ahve done that to some extent in this campaign. Also, causing revolts with spys can be a way to get rebels to help you take over factions, let them do the fighting and hopefully they (or the faction victor in that province) are weak enough to crush or bribe.