[EDIT]
Mouseclick problems all solved...
For the mouseclick problems (see point b in my response above), I have the perfect workaround (at least for me) by replacing the camera.dat taken from the Widescreen mod MaGui Final version (the one before v.3.4 was published).
After that, all mouseclicks work like in the stock game (correctly), now the
observation periscope will zoom at 1.5x-6x, the attack periscope at 1.5x-6x-12x (very good for identifying flags), the UZO will not zoom at x6.
These zoom factors could all be problematic when using Manual TDC with RAOTB disk, that's because AFAIK the zooming is not the right one for it, but it happens that I'm not a fan of high realism, so I will happily play Auto TDC in SH3 (the zoom factor doesn't matter), and Manual TDC in SH5
Listen, will I ever play SH3 again instead of typing in these subsim forums...guess...