Your iMac model is not the problem.
Apple's Maps application is black in Sierra, High Sierra and Mojave VMs on VMware Fusion 11 running on my 2013 15-inch MacBook Pro (which supports Metal, and has an NVIDIA GeForce GT 750M dedicated GPU if needed).
In my Mavericks, Yosemite and El Capitan VMs, Maps has a yellow background with no map data apart from dropped pins.
It looks like Maps requires a sufficiently capable GPU to display any map data. VMware Fusion still only offers simple graphics support in macOS VMs (no emulated GPU capable of supporting OpenGL or Metal). System Information in my Mojave VM doesn't say it supports Metal (other tests concur); OpenGL test applications only show Apple's software implementation, no hardware support from the GPU.
I haven't seen anything resembling a "no memory for more VMs" error so can't help with that question. As a test, I was able to run three VMs simultaneously (with 2 GB RAM each) on my MacBook Pro (which has 16 GB of RAM). Activity Monitor showed I had somewhat over 8 GB of wired memory and still had 3 GB of free RAM at that point, so apart from lack of CPU resources I could probably run a fourth one.
VMware Fusion still only offers simple graphics support in macOS VMs (no emulated GPU capable of supporting OpenGL or Metal).
Please see this answer from a VMware employee.
Perhaps that VMware now is making some progress thanks to metal, but even if that is the case, it still wouldn't help TS who does not have metal compatible hardware.
Wil| Author of Vimalin. The virtual machine Backup app for VMware Desktop Products
| Vimalin : Automated backups for VMware Fusion and VMware Workstation Professional
| More info at https://www.vimalin.com
| Twitter @wilva
| VMware Wiki at http://www.vi-toolkit.com
I think it was Pat Lee that told me they're going to improve the graphics in macOS VMs. How disappointing.
We're working on it. It's complicated.
If I remember right (it's been a couple of years) it's because Apple's driver layers don't provide an easy and consistent entry point - almost need to have emulation rather than virtualization. If VMWare can pull that off it'd be really something!
Thank you Michael.
Yet in Fusion 10 & 11 Google Maps works in Safari in my Sierra VM. Obviously, it's different graphical interface.
is it only technically difficult, or is it also politically difficult to collaborate with Apple?