Can you resize the toolbar? I'm old and it's hard to see the icons - I'd love to make them all much larger

Not sure if you are talking about the Dock, but since you mention "icons"

Try the following:

Apple Menu > System Preferences > Dock > Size

and/or

Apple Menu > System Preferences > Dock > Magnification

You can turn magnification on/off also from Apple Menu > Dock

You can, also, change the screen resolution in OS X System Preferences Panel under the Displays icon.

You can adjust the sidebar size in System Preferences > General > Large

The toolbar doesn't allow for customizations, but try System Preferences > Accessiblity > Zoom

Another option is to turn on icon & text for toolbar. Icons are generally easier to recognize. You can add cusotom icons to folders if it's a generic blue folder.

The new larger monitors make everything smaller. Try System Preferences > Display settings and choose a different resolution. I've never been happy changing from the default however. Really wish they still made a 24" monitor for the iMac.

Other links you might find helpful:

Center for Partially Sighted provides a lot of useful information to help you use your Mac.

Screen Loupe is a desktop utility that displays a magnified view of whatever is underneath your mouse cursor.

http://www.artissoftware.com/screentools/loupe.html

Macnifier shows a magnified section of your Apple Macintosh screen to help viewing up close. Freeware

http://subrosasoft.com/OSXSoftware/index.php?main_page=product_info&products_id= 15

Coloristic is a mouse over magnification program.

http://www.bubblepop.com/coloristic/