Actually for most globs and nebs you'll want something about 10-13mm... sounds like you need a bit of hands on experience before you start shopping for more expensive eps.
For a finder EP a 25mm Plossl is okay but a bit limiting with a 1500mm FL scope. You might want to grab a 32mm which gives the widest tfov possible in the 1.25" format. I recommend you start out with 32mm, 20mm and 15mm plossls and a 2x barlow. That will be plenty to keep you happy for quite some time.