Should I play the Harrwitz (1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Nc3 Be7 5. Bf4) as an alternative to the main line? Example game:
lichess.org/NvqQaNTT#whiteThat opening is completely fine. This opening is very positional and is similar to London opening positions. Whether you play this or the main line depends on where you like your dark-squared bishop, f4 or g5. Objectively speaking, Harrwitz and the main line aren't very different, so you can definitely feel confident about playing this opening.