SMD is surface mounted electronics instead of through hole, the processors are usually SMD. SMD means it's soldered flat onto a pcb and can be more tricky than soldering a switch or old LED that poked through a hole in the pcb. Some kids come with SMD parts installed, some it's an option, others do not even come with the parts at all and you have to source and then install them yourselves onto a bare pcb. SMD soldering is not super tricky if you've got some experience and a good iron, but if you haven't done much soldering it will give you lots of headaches.
Sourcing parts, you can still get an idea of what you need from looking at the kits, but again, the kits are not bad deals in themselves.
Some will say the GH60 is outdated, people still use Model M keyboards from the 80's. It's a keyboard, it inputs keystrokes, so long as it inputs keystroked it's not really outdated. Keyboards haven't changed much over the years, some switches have stopped being made, they added backlighting, some are programmable, and now some have underglow (which is really the only thing better about the DZ over a GH60), but ultimately, it's a keyboard. If you get a case that has a solid bottom, you won't see the underglow, so there would be no difference compared to a GH60.
This is why I said to not get caught up into the whole "custom is better", 90% of the feel of a keyboard is the switches, and you can change those. Some may have lighting, some have a heavier case, some may let you program the keys, but they all do the same basic function. Is a $900 custom keyboard really any better than a $40 Magicforce? It may feel nicer, it may type a little better if it has tuned switches, but you can put the same switches into the Magicforce for hundreds of dollars less, put some weight in the bottom and get the same typing experience.