Programmer new to Apple - How to efficiently switch between files in XCode?
Xcode does support tabs. You can add a new one by pressing Command ⌘+T, or go to View > Show Tab Bar to keep the bar open always so you can press the + button there. With multiple tabs, you can use Command ⌘+{ and Command ⌘+} to cycle through them.

As mentioned by bassplayer7 in the comments, you can also use multiple windows and cycle through them with Command ⌘+`(backtick) or Command ⌘+~(tilde).

Additionally, you can have multiple documents open in one window using Assistant editors. Either use Navigate > Open in Assistant Editor, or click the icon which looks like a shirt and bow tie in your toolbar to bring the editor up. Then, you can use the little + in the upper-right corner of the editor to add more.

The Navigate menu has several other useful options too, such as going through an editor's history, various counterparts to a file (headers, implementations, interfaces, ...), and switching focus between various portions of the window.

As for the navigator, use groups to combine related files for easier access. Use File > New > Group or File > New > Group From Selection to add a group and rearrange things however you want. You can completely remove the original groups created in the original project if you want, since they are just for navigation and have no affect on the actual project.