Are circuit breaker panels chosen by total amperage of all circuit breakers in the panel?

Most often if you add up all the breaker values in a panel they will exceed the rating of the panel. The theory is that you never operate each breaker to its full capacity. The panels are sized to the maximum current that is capable of being supplied by the electric company equipment servicing your house.

Correction: Panels are sized according to the outcome of a complicated process of estimating the maximum number of amps that are likely to be used at any one time. This gives you a minimum size and you install AT A MINIMUM the next larger size panel. I don't know of a maximum size by code but there are limits to what can be practically used.

In the absence of this complicated process, there are some rules of thumb that are substituted on houses. These range from 100 amps to 200 amps.