Before getting the hands dirty

I'm making my first hack on a HP 15 r110dx (spec). I've prepared the usb with required kexts and other stuff (followed the Dortania's guied). Now before actually booting off the USB, I have some questions to ask.

1. How well Catalina will run on HDD?

2. How am I supposed to format my target partition in APFS (1st point) ? It has no third party implementation (HFS+ has, by hfsprogs on Linux)

3. I'm supposed to have a 200+ mb partition, formatted fat, and flagged boot, as required. But that's the /boot partition used by GRUB, what will happen to GRUB then?

4. I neither have an Ethernet connection nor a suported WiFi adapter. I've extracted the HoRndIS kext from the pkg, will it work?

5. What I need to remember for multibooting with Linux?