7mm plossl is painful to use IMO, because of short eye relief and pinhole sized lens. A barlow will be useful with multiple EPs, so it's a good investment. You can get a good one for $99: Orion Deluxe 1.25", FMC Japanese barlow, with internal baffle like its bigger 2" brother. Try Sirius Optics.
Vingo, Re 4000 plossls, well, you did not say before you meant the old Japanese ones.
The current 4000s are fairly ordinary multi-coated Chinese plossls. GSOs are better.