Hello!
I work for myself and have been using Concrete 5 since last summer. I have built about 6 sites using it.
I think it is possible to integrate Google analytics - you can do it via the admin area I think but you could definitely add it manually too.
I don't think you can test-drive theme building, however, I have fairly decent HTML/CSS skills and although making themes was a bit of a learning curve, with the kind help of people on this forum I have managed to produce sites which have the functionality the client required without compromising the design and layout - something I have found impossible with other CMS systems.
In fact I have always had to employ a programmer in order to deliver CMS in the past but C5 allows me to integrate my HTML within the PHP myself. I have virtually no knowledge of PHP, but there is a collection of Concrete5 code snippets for Dreamweaver which is a big help and of course the extensive documentation and excellent tutorials on this site.
In order to deliver a very low budget site I bought pre-built HTML template from Themeforest (http://themeforest.net/) and in another instance I took an existing C5 theme and "hacked" it into shape to get the layout I wanted.
In answer to your last question, yes you absolutely can limit the available functionality to different users. You assign people a login and password and it can be set up very simply, while you retain the main admin account with full user access.
Best thing is to just give it a go. If you have problems, just search these forums. Chances are someone else will have had the same problem before and can help you.
Setting it up on a server can sometimes be a little tricky depending on your hosting company - I use webhostingUK (http://www.webhosting.uk.com/) and ask them to include the 'softaculous' script bundle which contains Concrete 5 in the hosting control panel. (some of their servers have an alternative script bundle which doesn't have C5 so you have to ask them) This gives you a very simple install within a couple of clicks. You can also set up C5 locally - I have it running on my mac using MAMP but for me, that was a bit more difficult to set up initially. Again there is loads of good advice on this site if you just do a search.

Cheers
Allison

Google Analytics is a yes. You can either hard code the JS script Google gives you in to the actual theme, or add it to the footer of every page using the dashboard from the Sitewide Settings page (where is says 'Tracking Code'). You can also find ScottC on the forums and ask him about a full integration package. I'm not sure if he's done with it, but he was telling me about it a month or so ago where it completely replaces the c5 tracking code with Google's stuff and changes some other things around and adds other things... I'm not the best person to ask about it, but you get the idea. :p

There isn't a CMS out there that is easier to make themes for. My work flow usually goes like this: design with Photoshop or Fireworks, then turn that into HTML/CSS/JS, add the c5 scripts. Pretty frickin' easy. I mean, you can pretty much turn any site into a c5 site by adding: Where 'Main' is the name of the editable area.

The permissions system is pretty extensive, monstrous at times. By default, advanced permissions is turned off, but you can add a one liner to the config.php file to turn it on: You can also disable the c5 Marketplace integration by unchecking it on the Sitewide Setting page, in the dashboard... or by adding another one-liner to the config.php file: