Yes I can see how it would take a long time to build on a Pi. My old Core Duo Windows box took ~40 minutes for a fresh build. My new 8-core "supercomputer" does it in ~ 4min. It's all about CPU speed and available threads.
There's no way your build will work on another computer unless you package up all the dependencies. My last commit fixes the Linux installer script -- if you add "install" as a target to the "make" build step of a Release type build, then it should take care of all the packaging for you and you should be able to move the whole build/bin folder to another Linux box.
The best way to install Qt is using their installer packages. Using a package manager (apt) isn't really recommended. But seems like you got through that.
QtCreator does all the build steps for you, no need to run qmake separately.
Good job remembering to update git submodules after checkout!

Cheers,
-Max