There are those of us that participate in various fan art and art assets threads that will disagree with you. I've yet to find a character that is a 100% match for the Daughter in Dating My Daughter in the various stores that sell Daz products. About the only thing that is a relatively easy match is her skin texture and hair (and clothing of course), but yeah her body has a lot of custom work done to it...
Elena is close to a 'base' Daz character, but she's been tweaked a bit as well. Same for Jennifer. Georgina is a bit more involved, and so far no one has found a close match for Olivia. Graham is Russel though, pretty much straight out of the box.
But, by all means, if you can point out the close or exact matches for these characters, I'm sure a LOT of people here want to know what they are! The fan art peeps will appreciate this!
As for most of the setpieces, well OF COURSE they are store bought assets! Time is money, and Mr. Dots obviously would rather crank out a bunch of renders instead of spend a bunch of time building a custom set. I can't blame him either.
As for the 'artistic style' that Mr. Dots chose for his renders, I'm sure some of that was for practicality/speed of render purposes. Or perhaps to fit inside of the graphics card memory of the system he had when he first started DMD. The SSS thing can be rather system intensive.
Anyways, back to the OP's question:
As others have said, yeah lighting can be tricky, so it's good to practice with different light setups until you find the one you like. I like emissive planes + HDRI myself, but the point + spot recommendations are being made for a reason.