I like your theme idea, and will join. It is a good, clean theme that is easy to comprehend, yet has a lot of design space to allow for different team lineups.
2 possible issues to consider would be these:
a) owners could decide to max their defence point spending on the defencemen (e.g. 6 d-men with ratings of 95, made possible by using 6 forwards with D ratings that average 55, or 12 forwards with D ratings that average 65).
This would probably result in a defensive minded league with lower scoring.
One way around that could be to state that the total max defence point spending for D-men is 450 (6 x 75) and the total d-point budget for forwards is 900 (12 x 75).
By separating the 2 positions, owners would not be able to stock up on the blueline.
b) make the language around the 3 scrubs crystal clear, so owners don't think they can use the scrubs to bring overall d-point averages down. One way to do this is to tell the owner who their scrubs must be, maybe pick 3 horrible players with huge PIM's, low shooting percentage, and a def of 5. Players no one would play in a 130 mil league.
Or if you don't care about owners doing this, assume that owners will have 3 scrubs with d-ratings of 5 to buy more space for the rest of the team. when you declare your D-rating budget, pick a number that accounts for this.
I like your theme, and hope it flies!