Quick question:

Is it legal to take sheet music of a copyrighted song and record it myself? This would be very time-saving to me especiallyfor music that involves a full-orchestra.

if the sheet music is still under copyright, you need to get the rights to record it legally. Thats why movies sometimes use remakes of songs, because its cheaper to get the recording rights for sheet music than to buy the song. (on a side note, even if a song is copywritten it doesnt necessarily mean the music is. If I recorded beethoven's 5th and had it copywritten, then only that version is under copyright, not the music for beethovens 5th.)