The number of circuits that can be on a 200 amp electrical panel varies depending on the manufacturer. If you have access to a 200 circuit panel there is no stopping you from that capacity as long as you are not exceeding the load of the service which is determined by doing a load calculation for your home.
A 200 amp service panel can be as little as 300 and as high as 1200 dollars depending on the size in which you wish to get. The cost to have a 200 amp service panel installed can vary depending on if you have the adequate size electrical wire or if you require a service upgrade to 200 amp.
A 200 amp panel is safely assumed to be enough power to supply very large homes. A house load calculation should be conducted if you truly wish to know if this size of a panel is required for your particular situation.
The difference between a 100 amp and 200 amp electrical panel is the size of the main breaker, the rating of the busbar in the panel, the rating of the panel enclosure, and the size of the wire supplying power to your home. A 200 amp panel can supply more power to your devices but a 100 amp panel is enough to do the job required.