Hi there!
This is a good start. However, may it would hurt looking at string writing: quartets and such. That would definitely guide you. Between Mozart, Haydn, Beethoven, and others, you have over 100 works. Next, I would remove the vocals. There is no real need for them. This is a piano quartet. Ergo. the main theme should go to the flute, the piano provides the accompaniment, and strings either provide the interact with flute and or provide background material.
Now MuseScore does not have the best samples out there. There are better ones. Musio and East west are step up if you are on the budget. If you have resources, look into getting a daw and score writer. You will need it.