Running VM for Xcode 11 what to expect?

Hi, so I am looking into using Parrelels or VirtualBox to install Catalina and Xcode 11 or 12 so I can get started with SwiftUI and build for iOS14.

Planning to build a lightweight social app with some chat functionalities, posts, and option to (video) call contacts. Will probably use some pods (which add weight).

(No I don't have the money to buy a new Mac and mid 2011 iMac is not supported to install a new OS)

Running this on an iMac High Sierra, SSD and 20GB RAM. I can allocate 17GB if needed to the VM and run nothing else while working on Xcode.

So, break it to me.....

1. How much will an average build take?

2. Would running it on my phone (not a simulator) build faster?

3. Will SwiftUI work cause I read some crash issues on VMs because of metal requirements?