Hey Aesthete18! Maybe it's late, but I would like to add three things:
> If you have the opportunity to ask a conductor about volume and balance, he/she will be able to give advice. Conductors are always "mixing" - so to say - those instruments when performing in different acoustic spaces without any electronic or digital aid.
> Find some record with the same instruments and with the kind of sound you want to achieve. Use it as a reference, comparing with your mix.
> It seems your music is all acoustic, maybe in a classic style, and it wouldn't be mixed as for example pop music. Try to do as little as possible as to effects. ( Regarding EQ's is best to only decrease on some frequencies which are disturbing.)
I wish you all success in your composing/producing!