You won’t harm violin strings with alcohol but you can harm the violin varnish. Make sure you if you use alcohol that you only focus on the strings and not the instrument itself. If you can get your hands on the rosin remover that Christy suggested above, that would satisfy both the strings and the instrument.
Regarding your question about too much rosin. There shouldn’t be significant buildup over just one or even two practice sessions. It sounds like you have too much rosin on your bow! Take your finger and swipe the back part of the bow hair. If you see a huge powder cloud that tells you need to take some more off as you had too much on.