Multiple editor tabs OK?

Data security is the reason to not have two Projects open in separate tabs at the same time.

Although it will seem like you have two projects open, as far as the system is concerned only the second one is valid.

So if you make any changes in the first project, it could have terrible consequences on the data.

The goal you've described of having the second window open as a guide - you could create a Reviewer account for yourself and have the Project open that way (it will be in Full Project Preview, not editing mode). 

You can also copy pages or entire learning objects into a new project. So basically, the content that you would want open as a guide could actually be used as a defacto template, just make changes to it (update the text and images, for example) and the "guide" things like location or styles, etc. would remain constant.

To do this:

1. Select the Home tab
2. Select Copy (in the New section)
3. Select Copy From a Project

A panel will open and you can browse or search to find the Project you want to copy from. You can select full Learning Objects or individual pages to copy. Pages can only be duplicated but Learning Objects can be duplicated or Shared, when Shared they use of the LOs is connected for updates.

If you have lots of pages in an previous project that are relevant to your new project you can copy a whole Project to start a new one new project. Here are the steps to do that.

And a Project can also be designated as a Baseline so it can be quickly used as a full template project to start a new project. Here are the steps to set a Project as a Baseline and here are the steps to select a Baseline when starting a Project.