Microfoe,
Welcome to the forums, we hope you find everything you need here!
The MK kit frames work just fine and I flew mine up until just recently with little to no problem. I suspect I was up against the max weight it could carry and it didn't blink an eye. The Droidworx frames on the other hand are a step up in terms of design and materials and they lend themselves a bit more to adaption of additional stuff. Give me one or the other and I could live with it just fine, but if money's no object then I'll probably go with the Droidworx.
Time to build depends on you, your experiences, your work habits, etc. My first Okto build took me a couple of weeks and that's probably a week longer than most just because I took my time and made sure every step was done correctly. The result was an amazing flying machine that survived everything I asked of it except for the simulated space shuttle reentry maneuver into a tree and even that episode left my electronics, motors, and quite amazingly, my camera intact (FWIW, the MKTR camera mount makes a wonderful reentry shield). All up with a camera mount, wireless equipment, a Canon camera, two batteries per flight, plus the MK kit I figure I had $5500 or so flying around every time it lifted off.
The upside to all this is that it worked great and has provided me with an immeasurable amount of experience with which I'm now building other things. The downside is that it was so expensive and important to me that I didn't really ever fly it for fun.
If you're brand new to this we could help with some of the basic decisions but at some point you have to just get started as this isn't as easy to learn just from watching others. A good way to start is to buy a basic quad whether it's MK or something else and just start flying it. Learn to fly a basic quad before ever flipping the GPS switch and you'll be assured a very fun and successful experience. The MK basic quad can be expanded to either a flat Okto (eight arms in a flat circular arrangement) or a coaxial quad (four arms each with a motor on top and bottom) at a future time and the same electronics and motors can be used.
Hope that helps!
Bart