I would initially look for a reliable host that automates install of WPMU and BP
There's no fantastico for WPMU, and BP is a plugin for WPMU, this plugin enables the one-click installation of bbpress forum.
Are there any good BP demo sites out there with which I can get familiar with BP from the end-user point of view?
You can find that in WordPress Showcase of BP sites
For more info about BP - http://buddypress.org/
To test-drive BP backend, get free account at - http://testbp.org/
I may need to get or develop a look-alike theme for the Buddypress portion of my site
Check out buddypress.org site for BP themes and there are some which have corollary WP themes bundled or offered as well.
whether BP is too over-the-top for a staid? golf club site
Ok, I didn't expect "staid" golf club members. When you mentioned 300 members, I assumed it was necessary for us to know how many users there would be. I have to say, I know many "non-staid" golf club members :-) If you or a webmaster is going to be the ones who will input everything in the site including classifieds for the members, then go with single WordPress installation.
Plugins like WP Event Calendar and Classified Ads Plugins in WP repository would help you get the information out. Besides, as you know WP and WPMU merge will be coming soon, BuddyPress will become a WP plugin as well.
Personally, I get "claustrophobic" when there are 300 users in one WP installation, I prefer to organize them in seperate WPMU blogs. But since it is not the case with the users in your end, yup, WPMU might just be over the top for a staid golf club :-)
In any case, you have enough time to decide on WP vs WPMU/BuddyPress/bbpress. I noticed you mentioned "relevant modules" in your first post. That's usually Expression Engine, Joomla or Drupal lingo :-) Are you more familiar with the other applications?