Were women who were more rotund in the 1800s considered more desirable?

This seems like it should be an easy question to answer, but it isn't, and attempts to answer it simply have led to a lot of bad history about social norms. Yes and no.

Certainly our modern "fit" ideal differs from that of the 18th and 19th century. (I'm bringing the 18th century into it because you mentioned Williamsburg.) Visible taut muscle was not attractive in women (or men, really) - instead, limbs, neck, and face were to have a soft roundness.

There is an elegant degree of plumpness peculiar to the skin of the softer sex, that occasions these delicate dimplings in all their other joints, as well as these of the fingers; which so perfectly distinguishes them from those even of a graceful man; and which assisted by the more softened shapes of the muscles underneath, presents to the eye all the varieties in the whole figure of the body, with gentler and fewer parts more sweetly connected together, and with such a fine simplicity as will always give the turn of the female frame, represented in the Venus, the preference to that of the Apollo. (Hogarth, The Analysis of Beauty*, 1772)

However, this can be (and is often) taken too far. Rounded arms were desired, but not flabby ones; painters of wealthy women often made sure to depict them in clothing that exposed their soft white arms, showing us that they all have a certain amount of body and shape.

Naked Venuses and odalisques of an era generally show the proportions considered attractive in private (emphasizing this because in everyday life, being corseted was a requirement for respectability and that shape was considered desirable when clothed). Odalisques of the 19th century frequently have that soft roundness, but they also have small waists (https://commons.wikimedia.org/wiki/File:MARIANO_FORTUNY_-La_Odalisca(Museo_Nacional_de_Arte_de_Catalu%C3%B1a,1861.%C3%93leo_sobre_cart%C3%B3n,_56.9_x_81_cm).jpg) and their breasts aren't very large. Their flesh isn't really disturbed by, say, the bed - it doesn't spread. "Rotundity" would be the wrong word - it implies a lack of defined shape, and they still found an hourglass figure appealing.

were women attracted by seeing men's calves?

Yes, men's calves were seen as an attractive feature! At least until trousers loosened in the mid 19th century. That said, I'm not sure emphasizing good calves or padding thin ones can be compartmentalized as being done to attract women; it seems to have been important to a man's presentation on the whole. A well-turned-out man was to have a good calf.

But beware of etymologies given out at historic sites. A version of "best foot forward" is used in Shakespeare's King John (Act IV, scene ii), and while men had been showing off their calves for a long time prior to that example, there's nothing particularly in support of it meaning "best calf forward"; it's clearly about luck there.

Edited for link badness