I checked the seed pack and found it's called "Tomato Beefsteak".
Strange name. Is it reasonable to expect 200+ tomatos this year? Can I
stay with the current 6" pot or have to change after sprout?

Beefesteak are awfully large. I doubt you will get more than a dozen or
two. Put it into a 5 gallon Home Depot bucket at the minimum.

Agreed: whether it is a generic beefsteak type or the old Scarlet Ponderosa
that was sold as Beefsteak for many years, The plants are large. The tomatoes
are also large, and tend to produce sparsely in a container setting. However
two or three dozen tomatoes per plant is a very good yield under good
conditions.