How is my Pokemon Diamond Team at the Moment?

I must say, you've done a really great job with your team's moves. Your choice of Pokemon is good too. Although, I recommend that you should train your Pokemon to Lv.32 because Maylene (Gym Leader of Veilstone) and Craher Wake's (Gym Leader of Pastoria) Pokemon range from Lv.27 to Lv.30. Since you're at Lv.25, you have to train more. Other than that, you're doing great!