R – SharePoint: Back up single page

I think your process is nearly as good as it can be. Without the designer knowing sharepoint all you can do is encourage them to make as many changes in css as much as possible. (then do your diff and apply it).

With ASP.Net and Sharepoint you are limited to how the markup can change if you wish to take advantage of certain components.

It's possible that you could convince the designer to use Expression Blend. But most likely unless they have development experience or you are willing to train them somewhat then there will have to be some developer engagement.

I trained my designer to use Visual Studio and it's made my life a great deal easier.

The page layout is default.aspx's backing "template". It holds the actual controls. Edit page layouts to move around controls etc. You can also create your own and bind them to content types.

Edit in browser basically means you edit the values of say the title control, or the content of a richtext fieldcontrol. This is usually done through sharepoint's front end web UI. You can also change a page's assigned pagelayout to a different one, i.e. have default.aspx use ArticlePage.aspx as pagelayout instead of WelcomeSplash.aspx. THis is done in the publishing console in the web ui as well.