Shameless plug: wincycle makes win/cmd+backtick to cycle between Windows of the same app work. This and iMessage were the two things I missed leaving macOS for Windows and so I solved them both for myself :)
As far as the Alt- switching goes.. that was honestly one of the more difficult things to solve for both Linux and Windows. For Linux because of the sheer number of DEs (a few absolutely hated it to allow certain remapping, had to send in patches for one of the DEs too!) and Windows because it initially appeared that the most simple remapping methods would clobber each other - but after working with Autohotkey enough it was apparent that it was indeed up to the task & I also kicked Sharpkeys registry hacking off to the side and no longer needed users to log off and back on. (Also makes pair programming a bit easier too.)