Hi Geoff,
Appreciate the issues with safety risks with respect to things that people can bump into in the dark, or fall off (ladders).
As Alex pointed out, in the city a fast focal ratio is not a good idea as it increases the brightness of the background sky glow - you're much better off sticking with f/10 or even f/15 (as in the scope I use, which is a f/15 maksutov) and that means cassegrain optics, not a Newtonian, to keep the physical size compact.
Since this is a visual scope, the solution I'd suggest is a Nasmyth-Cassegrain, on an altazimuth fork mount. Essentially it's a Cassegrain with a diagonal flat mirror in front of the primary mirror arranged so that the light beam comes out co-axially through the altitude axis of the mount. See
http://en.wikipedia.org/wiki/Nasmyth_telescope or
http://www.millseyspages.com/astro_p...a/nasmyth.html
http://www2.l-3com.com/ios/pdf/1meter_low-res.pdf
The beauty of this is that the eyepiece is always in the same place no matter where the scope is pointing. On a large scope with a permanent mount, the fork will be sturdy enough that you can easily fit a "tractor seat" on the side of the fork so the observer can sit, riding on the fork to look through it.
Finding someone to make this configuration is going to be difficult as it will be a custom one-off.
The focal ratio is a big issue.
As Alex pointed out, a fast f/ratio increases the sky background for extended objects (nebulae, galaxies, comets) which is not helpful.You can use higher magnification to reduce the background glow, but this implies the scope should have had a longer focal ratio in the first place, say f/10 or f/12 - which would be my choice.
As you know from the Planewave example to make an f/6.7 Cassegrain the secondary obstruction is huge - the Planewave scope is intended for imaging, and it will be really bad for visual use - you will notice a big black blob floating in the centre of the eyepiece. For visual you really want f/10 to f/12, and a smaller secondary < 30% of the primary aperture.
One way to get around the constraints of a cassegrain is to build a Mersenne or relay telescope where the cassegrain focus is in front of the primary and a positive relay lens is used to bring the focal plane out where it can be reached. This permits a fast compact cassegrain (f/6 is possible) while keeping the secondary obstruction small at 25%, and the final f/ratio can be varied from say f/6 to f/15 by moving the relay lens much like a zoom camera lens. It's the same principle as eyepiece projection.
With increasing aperture at a constant f/ratio, the focal length must also be increased so the useful magnifications provided by your eyepieces will increase, too. The downside with that is that the seeing at observatory hill isn't great due to atmospheric turbulence created by the surrounding buildings and the effects on what you see will be worse with a bigger scope than a smaller one.