1 - About "Open with" bug, I didn't encounter it since Win10 v1809 and also because I keep Notepad to avoid the "Open with - Other options" list to be empty which was the reason why it didn't work perfectly. I will try to reproduce the bug with my extreme wccf and let you know soon.
2 - About "servicing tool taking long" :
- Have you used "Unattended - Dism Cleanup" options ? .... if you not use it will speed up the installation by much
- Have you used "Service - Distributed Link Tracking Client Service" ? .... if you not remove it it will speed up the installation by much
I wish you to have very great day !