I'm hardly an expert on the current metagame, but...
Light frigates are your bread-and-butter: cheap, cost-efficient, and available right away
Corvettes are an alternative to light frigates: they come out early, they hard-counter long-range frigates (with the exception of Illuminators), and their maneuverability allows them to focus-fire with ease and confuse slower units
You kind of need corvettes, or at least the ability to build them in a hurry, if you go with LF, because LRF still defeats pure light frigate spam.
I've heard that Ravastra Skirmishers are significantly less efficient than other light frigates (Disciples and Cobalts); if so, how does this effect Vasari fleet composition?
I have also heard that Vasari corvettes do not compare well to Advent and TEC corvettes; if so, how does this effect Vasari fleet composition?
I have no idea if this is the accepted answer, but in general find myself leaning towards LRF/Flak with Vasari more than LF/Corvette which is what I usually do with Advent and TEC because of this. Not only do the vasari get LRFs easier than corvettes, but both of these units have phase missiles.
I doubt its used much in multiplayer, but I will say sometimes that repair ability on the Ravastra can come in handy. The heavy cruiser gets a better version though and with that massive wave bonus the Vasari loyalist get I think I'd build them over Ravastras still if you desire an unusual fleet composition.