I agree it's a bit strange that it never come up until now. I am having the same float-to-int issue on
setMinimumWidth
setMinimumheight
setMinimumSize
that are present in various .py files. I'll have a look if I can find more

About installing packages system wide, it's not an issue as I'm currenly on a "lab" machine that I am using just to test Armory and see if it compiles for me. Once I am successfull, I'll do the same steps on the actual "production" machine where bitcoind is running (which use the same distro), but even this one will be dedicated to Armory so there will be no conflict with other programs.
I might later be interested in the best way to move the actual program out of the build environment (i.e. "install") so I can have a stable version in use while at the same moment being able to test further developments. But it's a bit early for that
Thank you