Hi Alien,
I don't have any UW photos from this set-up yet, but it's pretty straight forward as to the configuration. The extension tubes come in a 16 and 10mm set. You stack them for 26mm, add the Sigma 60mm and you have exactly the same length as the 18-55 fully extended. It fits perfectly in Port 72. As to the limited focus range, it's not much different then when I went down with a 100mm macro and diopters; one is limited on what they can shoot. The magnification is considerably higher than the kit lens and the Sigma has some of the highest ratings on test sites, both in resolution across the f stop's and very low CA. So it'll be interesting to see what kind of results gets I get on the NEX7 sensor. Really not much macro choice for us NEX macro shooters in any kind of affordable range. I'm envy what 4/3 people have in that regard, but like you, I'm not changing systems any time soon.
In terms of working space, at the highest magnification I have a couple inches to work with in front of the lens which is enough for my lights. I hope this suffices until someone makes a reasonably longer macro like a 70-100. Personally after working with a 100mm in my old Canon rig on APS-C, I love to see a 70-80mm macro and some small wide primes to fit our 4.33 dome.
I'll try to put my rig together for you this week sometime and take a few photos of an common object (probably my mac keyboard, it's what I used) and show you the magnification comparisons and maximum distance you can get with only the extension tubes and no diopter. I made tests on graph paper a while back, but probably just easier to gauge the magnification on something familiar with a few photos.
Marshall