I'll get this on day one (provided the site doesn't crap out, of course), but it definitely needs some modding, particularly the pink cube and the flat roofs. The problem with the Quiddich store seems to be a combination of its large size, the eye-catching color, its prominent place in the box art and how too much of it is blank wall. The color isn't that bad (but the old pink or the flesh color could have worked better), but I'll need to add one or two more windows. Also, the pink stripe along the left of the ground floor (while the right is dark grey) looks a bit sloppy.
The flat roofs looks VERY bad, making it resemble an American small-town main street - with installed lights and some HDR photography it'll look just like a Kinkade painting. In pictures the buildings actually has four or five floors (often protruding over the lower ones) topped with elaborate sloped roofs, here they've just left this out. The parts they have included may be movie-accurate, but by leaving out the roofs it doesn't look like Diagon Alley at all. As such they'd been better off going for the "book" look with two- or three-floor buildings, so it looked more like a combination of the old DA set and the Medieval Market one.
Regarding the technic holes, I believe the sections are supposed to fit back-to-back to make complete buildings - Olivanders would fit with Flourish (at least if the stairs are removable) and Quiddich would fit with Weasly's (which also would explain the unsightly half-floor on top of Quiddich). I've actually done the same with most of my modulars for years now (to make the interior more accessible), except I also add a second set of holes further up (around the bottom of the upper floor) to make the buildings hold together when moved.*
Is the hairpiece for Olivander and the ice cream guy new? The older similar one (used for GBHQ Wenkman and Dimensions Dr Who) has more prominent sideburns. Also, when people talks about the "Dirty Harry" figure, it really reminds me of something like: "I know what you're thinking, did I cast six spells, or just five? Well, do you feel lucky, muggle?"
*See these old Norwegian forum posts for some examples:
City University (Town Hall) - http://brikkelauget.no/diskusjon/viewtopic.php?f=3&t=3977
Parisian Restaurant - http://brikkelauget.no/diskusjon/viewtopic.php?f=3&t=4147
Detective Office - http://brikkelauget.no/diskusjon/viewtopic.php?f=3&t=4209
There are some even older ones on my Flickr page (https://www.flickr.com/photos/axeleng) - haven't updated it in ages.