Were all carnivorous dinosaurs huge?

No. Some predators were very large, but others were much smaller and lighter.

Do birds belong to the theropod line?

Yes. Birds emerged from the theropod dinosaur lineage.

No. Body plan, size and habitat point to very different strategies.

Mainly from teeth, skulls, jaw mechanics, stomach contents, bite marks, coprolites and comparisons with related forms.

No. It is the most famous one, but not the standard model for all theropods.

No. It looks more like a specialized variant that broadens the classic theropod picture.