Use the Wayfinder snippet for your menus. Download the doc for it and dig in. It’s quite flexible, to the point of actually being a mini-application on its own. By default it will generate a simple nested unordered list which you can style as you please in your CSS.
As far as the one-or-two column issue, here’s where a TV would come in handy. It’s a bit difficult to understand TVs in the beginning, but it’s well worth it.
Create a TV , give it a name (style) and description (style chooser) and just leave everything default, except in the "default value"; in that one put the name of your CSS file for the main use, I presume that would be the 2-column layout. Make sure to check the box at the bottom to assign it to your template! Now all documents using that template will have an editing field for the TV underneath the main content editing area.
Now put the TV’s tag in your template’s head where you have the link to the css file.
<link rel="stylesheet" type="text/css" href="assets/templates/mytemplate/[*style*].css" />
Most pages will be perfectly happy with the default value you specified when you created the TV.
Here comes the TV magic. On those pages where you want one column, just edit the TV (under the main content editing area) to have the name of your single-column css file. Now those pages will get that file linked to.
You can get fancy and make the TV a dropdown so that when you edit the pages you can choose the css file from the dropdown, but we’ll keep things simple for now!