As much as I've looked, I can't find the hardware requirements for running minishift. Nothing mentioned in the Container Development Kit documentation, and the OpenShift documentation only mentions hardware requirements for production deployments.
I've been following RedHat's advice on running their Container Development Kit with nested KVM.
https://developers.redhat.com/blog/2018/02/13/red-hat-cdk-nested-kvm/
I may be pushing the limits. On a MacBook Air with 4x1.7GHz & 8GB RAM I’m running Fedora 27. Gave 6GB RAM & 2 cores to the RHEL Server and starting Minishift saw that it was giving 2 cores and 4GB RAM to VM. It took about 30 minutes to download and extract the 4 docker images. Things got progressively worse from there.
I’m trialing OpenShift Online. Would I run into a world of pain using Minishift directly on Fedora?
You would be better of running Minishift directly on Fedora 27 with KVM. Personally I use Minishift on Fedora 27. Using nested virtualisation will not give optimum performance as Minishift creates another VM to provision the OpenShift. So I will not recommend using nested virtualisation for Minishift. With the default settings i.e. 4GB RAM, 2 cores and 20GB disk you should be able to run few simple micro services on it. The resource requirement comes from the application you are trying to run on top of it. So if you are running an application which needs a lot of resources then you need to increase the resources to Minishift.
Once you know how much resources are fine for your application, you should save your configurations using "minishift config set" command. It will persist the settings across start/delete.