I'm assuming you probably already know since you're making WineGUI, but older versions of Office (particularly Office 2010 32bit) are pretty simple to get working. Just need to install some dependencies with Winetricks.
I'm impressed how well wine-wayland already works. Some games still have issues with mouse locking, at least Overwatch doesn't register the at all. But as they said, bugs will be fixed over time.
I have issues with game resolution, when using Wine-Wayland the only resolution available is the one already set for my display, which renders FSR completely useless. As well as this little cursor render bug that sticks a frozen windows cursor on the screen, though I've been able to work around this.
Are Wine apps ran isolated? Because we basically have no viruses on Linux, but I imagine running random of course legally obtained games may be very risky
No, the Linux filesystem is usually mounted as Z: in wine. Sandboxing through e.g. flatpak/bubblewrap with permissions set to only allow access to ~/Games should protect from many viruses.
I'm on 9.0 staging and can use wine with Wayland, but not everything works, window bars etc look somewhat off and some games don't start at all, like Stardew Valley. Other games I tried failed to hide the cursor. Others worked just fine.