On the genitalia thing, there are '3rd party' gens that you can also get (New Genitals for Victoria, Dicktator, Golden Palace, etc.). Most of those are offered through Renderotica. The art assets section of this forum has details about those.
The 'default' Daz gens that come with most of the pro bundles can get the job done (I think Teen Josie, Tween Julie, Tween Ryan, Teen Jayden, etc. often do not include the gens, you know to discourgage teen porn or something), but the aftermarket ones generally have more pose options than the 'Pro' gens.
The Pro bundle characters, depending on their popularity, often are prerequisites for other characters that come later, after their pro bundles are released. You can try dialing in the character without the 'base' character, but it'll look different of course. Sometimes not much different at all, sometimes VERY different.
But yeah, the main 'draw' of the pro bundles is that you get around 8-12 products in the pro bundle including the base character. The bundles often include hairstyles too. When products are 'newly released', the pro bundles often have additional discounts that make them more interesting to the Daz buyer, and of course once those bundles are much older, sometimes they go on sale. Of course, if you acquire your assets via other means, the pricing thing won't be as important to you.