It is both. They have a very large hangar on the left of the entrance with lots of planes on show. You can walk through one or two and read lots of information. There are lots of other buildings to go into - one is the American area, another land artillery. It is all really interesting and tiring, so put on comfortable shoes😬. There are a couple of small buildings also. On the external there are many planes to look at and read their history. They also have a cafe with inside and outside seating - and a children's play area. You might need to re-visit to see it all.

Yes their is a C47D at Museum

The best way “on the cheap” is to walk. There is a station south of town(Whittlesford) that is not too far from the museum and you can walk to/from there. You’ll be walking along a busy road and there is no sidewalk or footpath, google it first to make sure it’s worth it to you to save a few pounds though. But it’s doable. Next cheapest option would be arrive at Whittlesford and call a taxi from there. If you can’t reach one, call the museum and ask them to call you a cab, they are very helpful. A cab from here will be much cheaper than a cab from Cambridge.

I recently visited here and was there for at least 5hrs but that is most likely because of personal interest if your just looking to walk through everything and not really read into it then I'd day about 3hrs tops