I'm only learning this stuff myself, but I'm starting to figure it out (slowly). If you want a female model with great genitals then the Genesis 8 model with the Golden Palace genitals addon is my go-to, but there's nothing much I could find that even comes close for the other genesis models which is a pity because most of the best body morphs seem to be for genesis and genesis 3 - I can't do non-standard body types (BBW, SSBBW, midgets etc) very well with the genesis 8 as Daz Studio seems to be designed for users in California where everybody looks like a 6-foot tall silicone-enriched Barbie doll.
Genesis 3 on the other hand has a great many body shaping morphs available, so that's the one I tend to use for these unusual body types.
You can buy pre-made character models which add a bit of variation (they still all look like Barbie dolls though) but come with realistic skin textures and makeup effects. The only problem with these is that most of them cost money so unless you've been on the internet long enough to know where to find all the stuff for free (well, most of it anyway) then you could end up spending a LOT of money on this stuff. As others have suggested, beware of EXE files on free sites. Important safety tip - Do all your 3D work on a seperate system that doesn't have an internet connection, and back it up regularly (I do mine once a week)
A lot of the commercially available characters are for the old Victoria 4 model (and its variants - V4.2 for example) rather than the newer ones. SOME of the content that comes with these is interchangeable but not all of it. Hair can be a particular problem on the model it wasn't designed for - The Fit To... context menu option will help but it isn't always reliable.
And on the subject of hair - MOST CHARACTERS DO NOT COME WITH HAIR - Something to bear in mind, especially if you're paying for this stuff rather than getting it from torrent or other file sharing networks. Also, the example pictures on some of the sites (I'm looking at you, renderosity.com) show beautifully rendered images (not sure what renderer they use by my results don't even get close to theirs) of the character WITH hair but you don't get the hair in the pack. Worse still in most cases they don't even tell you what hair addon they used in the render
But the worst aspect of all when it comes to Daz Studio is the absolutely CHAOTIC file hierachy - it can be VERY frustrating trying to find what you want once you have a lot of addon content installed. Seriously this REALLY needs to be sorted out. It's not all Daz's fault though - much of the trouble comes from the need to make Daz Studio compatible with older Poser content, but it can REALLY mess with your sanity at times!
Like I said, I'm only just learning this stuff, and the learning curve is steep, but if you stick with it, you WILL start to work out WTF is going on