Do not play strictly to a metronome. Most professional scores, such as the Robert Lunn arrangement , specify playing "freely throughout" (rubato) to allow the melody to breathe. Recommended Tab Sources for Further Study
If your bass notes sound louder than the melody, lighten your thumb stroke. The bass should act as a soft cushion underneath the vocal line. To help refine your arrangement, let me know: nessun dorma guitar tab fix