The registry is NX-76884, but that doesn’t necessarily mean anything in Star Trek regarding years. If you want to pretend it does, that means the ship had been under construction for a year or two when Voyager returned, and it could have been retrofitted with the new technologies it brought back from the Delta Quadrant before its launch in 2381 or 2382.
Nice to see ASDB.org's Andromeda-class in there. It was smaller than expected, for a Galaxy contemporary, but still a nice design. I tend to like many of their designs (maybe not wholly sold on the Wambundu, and some others - maybe not the Bradbury entirely, either?) The Defiant I usually interpret as around 120-122 metres. As for the Protostar, it looks comparable in size to the Nova a lot of the time, from the outside, and scaling windows, etc. Compared to the new USS Dauntless though, it seems 1/4 the size or less, in a case of maybe overly dramatic scaling.
Scaling has never been a strong suit for Trek. That depiction of scale feels accurate enough. Protostar is definitely a smaller ship. Being Defiant-ish in size is generally ok, although it is odd given how large some of the interior rooms are. It DOES seem like the ship was designed to operate with a minimal crew, and we've seen the protostar drive/engineering doesn't really take up that much space, so I guess they had a bit more room to play around with.