Hi, Welcome to the Ventura
I have a 75 that I have redone (and am still tweaking). I benefited greatly from the help of other owners of all types of fg trailers.
You asked a question about the roof. My roof is just like that. It is higher on the ends but i tested it and water did not pool at the fan so I consider that ok. It is just age, I think. I did reinforce the roof from the inside as many others have done and it retains the gentle curve so I am happy with it.
Just a caution about the tall cabinet as well as the uppers on the other side. Other much more seasoned fg owners than me have warned that these are structural and removing them can compromise the integrity of the shell.
Like you, I wanted a more open feel so I moved the tall cabinet to the other side and made a low cabinet having a one piece side support that runs up to be part of the upper cabinet. (see photos). So far, after over 20,000 kms of travelling, I have seen no evidence of cracking or other damage.
Hope this helps. good luck with your new venture.