3) The little plane - I don't think it is a plane, it's merely some random object sticking out of the water.
The MoD not only identified it as a plane, but specifically a Harrier. See the Clarke article I linked (
https://drdavidclarke.co.uk/secret-files/the-calvine-ufo-photographs/)
5) If this is the "best" photo - where are the other 5 that weren't the best?
According to the interview with the owner of the print, more of the same, but with the aircraft in different positions. See;
As to going to the original location, perhaps MoD photo interpretation (JARIC, who were sent it) did do that. If so, no record survives (but then, no negative or print of this survived in the archives either; just a fax copy).
Clarke and his chums claim to have found the location;
https://youtu.be/IgekUVzMSCc?t=2121
If so, it would tend to suggest that it's not a view looking down with a reflection (which is still my preferred explanation), although of course it might not be the correct location. Alternatively, as I noted above, Metabunk have proposed that the UFO is actually the peak of a mountain surrounded by dense mist/fog. Not sure I buy that, but either way that 'aircraft' is definitely brown and green, with flecks of white (possibly cloud or mist).
Then we have Clarke's claims that someone from DI55 confirmed this was a US experimental aircraft and that documents he'd obtained via FOI supported this; see the same article with a snippet from one of the documents;
https://drdavidclarke.co.uk/secret-files/the-calvine-ufo-photographs/
Edited for clarity and links. Edited again to say on reflection I still don't get why Clarke is suddenly convinced. Other than a nicer pic, what's changed since he wrote this above-linked sceptical take?
Edited yet again (sorry) to highlight this post;
https://www.metabunk.org/threads/calvine-ufo-photo-reflection-in-water-hypothesis.12572/post-276648
Despite what that poster says, that is quite convincing for me i.e. the UFO is likely (as previously suggested) a reflected piece of land in the water and the 'Harrier' is quite possibly a rowing boat with a hunched over occupant!