What do te think of these proportions (as in body proportions) in this sketch I drew? Are they realistic?

her thighs aren't to realistic, and her waist looks a little boxy otherwise good job :)

Yes

waist is too thin, superiore, in alto part of the legs too long

Not in the least.
The thighs are WAYYY to long, the waist is too short, the shoulders are to broad. The arms are also quite short.


So no.