[Arran]

Since some of the missing bits of wood are pretty large (up to ~0.25") the filler will need to be structural - so I'm thinking of using epoxy filler putty that Mohawk makes - does anyone here have any experience with this or a similar product?

Also, any thoughts on what kind of wood would've been used for the legs?

It was either tulip poplar or maple, by the looks of things, very little grain in any event. If the missing chunks are large you could try to patch them with some chunks of a similar wood, though one of those epoxy based putties might work just as well since the legs will be covered with shading lacquer anyhow.
Regards
Arran