Best approach to foundation for my design?

I am a photographer interested in developing my portfolio website.

I'm looking for some advice on some 'best practices' to get started with my design so that it will be simple to manage and not require a complete rebuild to add (relatively simple)functionality for my customers, in the (near?) future. I'm also wondering what content management systems would be appropriate for my small site, but not limit my flexibility for design(graphically and extensibility speaking).

Why should/shouldn't I go the typical photographer route and base at least the public side of my site on Flash(keeping my ideal specs for my gallery in mind)? I have access to CS4 Master Collection through my school, so I'm not worried about the cost to buy in, there.

The ideal site design framework I am looking at right now consists of two basic sections; public and client-only/private.

***Public
-Landing page
-Mission/About
-Contact
-Possibly a blog
-Gallery -- This will be a page, or series of pages with a modest list of thumbnails on one side and a particular image displayed and changed via AJAX/Flash in the center. Ideally, in addition to typical navigational controls, this will have the following features...
*Javascript/AJAX or Flash to prefetch the images so that the load times between viewing different images is reduced or eliminated as the user clicks thumbnails or lets the slide show play.
*Gallery contents are managed through some sort of CMS, instead of editing the html/js/flash to change/add/remove images and captions. I'm already figuring that I am going to end up building the image viewer myself, since I have yet to find a script that does exactly what I'm looking for, including Highslide.
*Unique URLs for each image(even if it's just a variable, like "?gallery=editorial&image=2"), so that a particular favorite can be bookmarked or linked to other people with out having to describe a "roadmap" (I want to eliminate what I see as a very common and major faux pas in photographers website design: "Hey Potential-Art-Buyer, check this out! Go to <site>, click the gallery, go to page 2 and click the 3rd image down in the 2nd column...")

***Private
This area is pretty simple. Aside from administrative access, I would like to be able to...
*Serve commissioned content to clients so they can retrieve it at their leisure. It would basically just be a unique page, generated for each user according to a database of what files are theirs.
*Page arranges content according to job folders and allows the client to download any files I've prepared for them.
*Record that the client has logged in, which files they have downloaded, and when.
*Maybe even allow them to leave comments for individual files in a simple discussion format.

It would be pretty slick to have administrative access include tools for social networking, like automatically updating twitter/facebook status with my blog post headline...

And, of course... Customizable templates!

Is there a light weight CMS that addresses these considerations? Can anyone offer suggestions on what I don't know, but maybe should think about? (Especially what I don't know that I don't know! ) For example... I know nothing about SEO.

Oh, I'm not entirely sure what my webserver is based on, but let's assume Apache, for now.

Thanks for taking the time to read my post!