The Lisa doesn't have an alt-tab function for Window management, so I haven't added one. Also, it would be difficult to use those keys in particular because it would conflict with your system's alt+tab keyboard shortcut.
When you select text in a textbox, the keyboard should input text. Also, individual menu items have their own keyboard shortcuts. If you're on a PC, it defaults to using the Control key as the "Apple" key. If your on a Mac, it defaults to using the Command key. This option can be changed in the preferences app in the "Set Conveniences" pane.
I don't mean Alt+Tab, just Tab by itself to move focus through the widgets in the current window. I don't know how it's supposed to work on Lisa, but pretty much every TUI or GUI I've seen from early 90s onwards had full keyboard navigation support like that.
Nope. AFAIK, full keyboard navigation was first developed for Microsoft Windows, as a necessity, because they couldn't rely on people having a working mouse.