Some ill-informed and similarly newbie comments on your posting (corrections please!).
1 I didn't experience the postgres 7.2.3 /Open ACS 4.5 calendar problem you mention. I am also using 7.2.3 with a 4.6 system and calendar works fine. The only issue I had was with OpenFTS which was hard-wired to OpenFTS 2.1/Postgres 7.1.3 and needed some fiddling (thanks to Dan Wickstrom) to get it working. I beleive these are now fixed in CVS.
2 Arsdigita is no more. Some of the forums are are kept at RedHat. Reporting bugs should perhaps be better documented in the docs, but this is open source (read unpaid) and resources are always an issue. That said, I think Roberto and Vinod are progressing things rapidly.
OpenACS.org is the best place to report things.
5 I have found that the daemontools start-up a revelation, easy, reliable, and controllable. Is it possible to get the postgres start up with daemontools, or does it have to be in the usual boot formats?
7,8 It took me a little while to understand the "mount" thing, too. Installing OpenFTS as per the "Next Steps" doc, gave me some better understanding. In most cases, a new application sets up a new instance of the module, while mount/unmount will allow locating/ un-attaching/ relocating of an existing instance. So, if you have a calendar at a url, you can unmount it from there, then remount it at a different url witout losing any data.
13 I think that this would be good, too. I'm going to work out how to add general-comments, and if successful, will post it.