The most common question we get involves how many LEGO parts we used in a particular layout. The answer to that is really hard to calculate exactly for all sorts of reasons, but over time we have been able to come up with some rough estimates. We find that, on average, a quarter block module uses 500 parts. Therefore an average full block module uses about 2000 parts. Extrapolating out then a pretty small layout of 4 by 4 square blocks would be 32,000 parts (4 * 4 * 2000). Our largest display as of the time of writing this answer was at BrickWorld Chicago in 2016 where we had a layout that was 18 by 7 blocks, for an estimated 250,000 parts (18 * 7 * 2000 = 252,000).
Most often people appear to be referring to an entire layout, in which case the answer is that we built the first modules in August of 2008. However since the layout is modular the more interesting question is about how often it took to make specific modules and the answer to that is: It varies. A lot.
Partially the amount of time taken depends on the designer. Nathan tends to design much more slowly than Jennifer and can take years to work on a module in LDD or LDRAW before finally putting physical parts together. ( For example Dudley Plaza was in LDD for about 14 months before the main structure was built). Jennifer has been known to put together up to six modules in a single (fairly long) day though more usually can build a single full block module in about 8 hours total work.
However some models are just more complicated than others. While the entirety of the Micropolis Gorge complex took about five months to design and build because of it's size some aspects of it took longer than others. The flyover bridge took an afternoon while the waterfall took about two weeks. The Ivy Building took an uncharacteristic several days because it uses some fairly complicated SNOT techniques.
No. As of the time of this writing The LEGO Group has never produced a set based on the Micropolis standard and it seems unlikely they ever will. All of the buildings have been created from the imagination of individual designers and are not copies or modifications of existing sets produced by The LEGO Group.
We often somewhat flippantly tell people that it can be any city they want it to be. The modular nature of the Micropolis specification in general and the whims of the person or persons who are assembling a particular layout in particular have a huge impact on which modules get placed where and in relation to other modules. Add in variability in the modules brought by other contributors and the amount of space at a particular display and it is very literally never the same city twice.
Inspiration for a particular module can come from nearly anywhere. Sometimes in the case of a module like CenturyLink Tower it is a closely inspired replica of a real building in downtown Saint Paul, MN though often the scale is modified to fit with budget or aesthetics. Many building ideas come from a certain class of building and the Octan Refinery, Miles Tower, and Cemetery are good examples. Still others come from one of us really wanting to have something like a Children's Museum or a Solar Power Plant and then coming up with what we think that would look like.
It should be noted that one should be careful when using a phrase like, “That couldn't possibly exist in reality.” Several of the strangest structures to have shown up in a Micropolis layout have been based closely on real buildings. A perfect example is Thomas Anderson's replica of the Atomium that was debuted at the Science Museum of Minnesota display in 2015.
Mostly BrickLink. We also buy a lot of sets and use parts from them after we've built them once and taken them apart. As with many LEGO hobbyists with medium to large parts collections we try to keep all of the parts organized for ease of finding them to be used. Having a big tub, or even several big tubs, does not scale well when you are looking for one particular part in one particular color amid hundreds of thousands of other parts. Nathan tries to spend at least 15 minutes every day sorting parts just trying to keep up with the natural entropy of leftovers from construction and new sets or BrickLink orders.