hey so, don't touch classical music before your mapping skills will be at least decent
yes you can learn how to time variable timing songs, but the process of timing itself takes way too much time and effort and is not worth it considering you've just started mapping and when you finish the map, it will be simply bad (don't take this as insult, everyone's first map is bad), and in result won't be able to push it or do anything else with outside of getting minor feedback. mapping variable timing also differs quite a bit from quantitized stuff as you need to accomodate it to the timing changes, to make gameplay experience as smooth as possible, which you shouldn't think about as new mapper either
so yea, i'd recommend finding some different stuff that's actually quantitized so you won't waste effort on timing it. how about artcore (stuff like xi and sakuzyo do)? they aren't exactly beginner friendly either but they also have a lot of piano usage which you might find appealing if you like classical. recent unlucky morpheus covers (like
this one) also have a lot of violin and as far as i can tell they're single bpm too. that's some quick examples i can think of (of course if you have different genre of music you like, just go with that instead)
so tl;dr learn the basics first, then move onto classical stuff
if you're really desperate on learning them on classical songs tho (which again, wouldn't recommend at all) then at least use timing from some of ranked stuff - classical is now a website genre so you can use it to easily find those