g1smd - 8:23 am on Dec 13, 2012 (gmt 0)
The redirects look good, especially with the OR construct arranged in groups of four (and that is the same answer that I saw lucy add in another thread mere minutes ago).
If the URL requests are extensionless, then the rewrite to a static "cache" folder looks good. With some fancy PHP scripting it's also possible to automate the generation/creation of those static files each time the database copy is updated/edited/changed.
Once you know PHP the features you can add are unlimited.
Don't worry about the number of rules in htaccess. As long as the code is efficient, this stuff is blisteringly fast. The one thing to avoid for sure is (.*) at the beginning or in the middle of a RegEx pattern.
The biggest problem with having a lot of redirects in htaccess is not so much the performance but that it becomes difficult to maintain a big file. If you are editing it often, the likelyhood of making a typo that brings the whole site down (if you are lucky, so that you spot it quickly) or a part of the site down (which you don't spot for ages until your rankings are drying up) increases rapidly.