I am not particularly fond of the "free to play" economic model DAZ uses where a base figure requires DLC just to be minimum useful. I would have paid $10 more for Victoria 4 to get Morphs++ bundled with her because she's impractical without that package (remember, it includes basic expression dials, not just FBMs). 

Price Project E fairly but include robust functionality, don't make expressions, general head morphs or the basic FBMs an add-on.

An optional deluxe package can bring additional content like texture maps, basic clothing (matching those FBMs), one hair model, magnets to refit V4 hair to PE, props, poses and expressions and it'll still be a hot seller because we know you made them for the figure. Sell it as an add-on and charge 10% less for buying it as a bundle with PE.

The key to getting people to leave behind one figure for a new one is:

• improved functionality with more base features 
• sane figure subdivisions and mapping (Scarlet and Dawn tried to be clever, it didn't pay off)
• wished-for material zones that play nice with the surrounding areas (e.g. makeup zones like lips and eye skin area have an additional transmap or similar to blend with the base face skin material) 
• available bundle pack: no waiting period for content to make the purchase practical immediately
• 10% discount on bundle pricing when purchased with the figure

After that point the rest is just frosting on the cake.