1) 'it will fit nicely into the whole picture of the boat..
"picture" the translation is too literal, sprobuj "idyllic scene"
2) ktos sie stal dla kogos PEWNEGO RODZAJU przyjacielem?
'you've become SOME KIND of a good friend to me'
huh?
one of my closest/dearest/best friend(s)
a [very] dear/close/important friend
to use qualifiers such as " some kind/sort of" with the concept of a very close or best friend, sounds like (at best), an inarticulate teenager
3) jak przetlumaczyc: 'kiedy poczulam sie samotna, pomyslalam o tobie jako o osobie ktorej chcialam o tym napisac' moje tlumaczenie: 'when I felt lonely, I thought of you as the person I wanted to write about it'
-awkwardly phrased, at the very least, add "to" after "write": write to about it
it would be better to re-work the entire sentence