Q1. have a XXX look to it, can't understand the to it part.
What's the function of to it and what does it refer to?
what does it refer to?
First I will answer Q2.
"It" has to refer to something, in this case the subject of the conversation is the swimming costume and this is most likely to be the "it " being referred too. Also it is something that can be worn. The only item that can be worn is the swimming costume. Therefore I can say with certainty that "it" refers to the swimming costume
**have a kind of 1950s **look to it****
The above sentence can be said to mean: It (appears to) have 1950s (connected with) it (the swimming costume)
Kind of and sort of are very common expressions in speaking. They soften other words and phrases so that they do not appear too direct or exact. Cambridge English Dictionary
look: verb (SEEM); Cambridge English Dictionary usually + adv/prep; to appear or seem:
to: preposition Cambridge English Dictionary (CONNECTION): in connection with:
it: pronoun Cambridge English Dictionary (THING):used as the subject of a verb, or the object of a verb or preposition, to refer to a thing, animal, situation, or idea that has already been mentioned:
At that moment, his face had an unexpectedly vulnerable look to it.
At that moment, his face had an unexpectedly vulnerable appearance connected with it.