I just in the gnome Box/Virtual Machine with 2GB RAM 17 GB disk, at the mount to /mnt/funtoo step but then drop back feeling it's better to ask first here
https://www.funtoo.org/Install
How's or is it simply doable to install Funtoo via installing inside Virtual Machine in place of USB ?

Please help me give the realistic useful answer

You need more disk space. And more RAM. Gentoo (Funtoo) can be run with 2 GB of RAM and 3-4 GB of disk space, but you can't compile like this and have portage and distfiles installed locally. 17 GB is OK, if you have portage and distfiles on NFS. You need 2 GB of RAM per CPU thread, 4 cores need 8 GB. You can compile with one thread and 2 GB of RAM, but it takes forever.

I built two Gentoo in VMWare, then transferred them to hard drive for lack of internet through ethernet, only wireless internet here. I think the multilib Gnome I was able to build in 20GB disk. But not the no-multilib KDE, I eventually had to go to 30GB. I still have both in vmware also, as it sits, the KDE pure 64 takes 12GB of space, Gnome multilib 9.5GB.

You need 6.5GB of free space to compile Firefox, so if my KDE was in a 17GB partition, I would not be able to upgrade Firefox. If you install KDE Plasma addons, you need 10GB free space to compile qtwebengine. So to update qtwebengine which cost me some 6 hours in VMWare with 8GB ram allocated to the VM on a completed build of KDE Plasma, you need around 25GB and a third wave of COVID-19 (for the time required).

That's the way it goes with Gentoo and the likes, you need lots of resources, memory, CPU, disk space and time.

If you don't have all that then you need to get creative, I had such a computer once running Gentoo, 2 GB of RAM and very weak CPU. I compiled in NFS chroot using the resources of my much more powerful desktop. Worked great.