Q1&2
For web-based KVM manager, you can try Proxmox. Instruction for Debian Squeeze is here.
It has command-line tools, but not text-based -- menu-driven.
Q3
You should setup a small environment and try it out. Then set out a goal and implement it.
Q4
There is no accurate answer/tutorial for this. How tunable your KVM server/client is really depends on how many resources (cpu/ram/storage) are available.
Q5
Again, this depends on your environment and it is multi-layers/devices, e.g. routers, firewall, ip-tables, password policy, access policy, etc. I am not aware of a single GUI, web-based or not, that can handle all of that including the KVM. (OK, there is cloudmin, but I have no experience with that at all)
In qemu/kvm, you only get a GUI if you attach a video card to your VM and if you don't expose it as SPICE/VNC.
For instance, you can do (zsh syntax, with grub2):
grub-mkimage -O i386-pc -c =(print -l serial 'terminal_input serial' \
'terminal_output serial'
) -o grub.img configfile biosdisk part_msdos part_gpt ext2 \
linux test serial halt minicmd cat
And start your VM with:
kvm -kernel grub.img -hda yourdisk.img -nographic
From the grub prompt, load the kernel from the disk passing console=ttyS0... option or equivalent on the system you're booting to have the console on serial. Remember to add a getty on the serial line as well.
Assuming you're running Linux in the VM, you can then update its grub config to display on serial and boot a kernel with serial console, and then you can boot your image disk directly without that grub.img.
To access the qemu "monitor", type Ctrl-Ac (where you can add/remove devices...).
You can have the serial port as a unix domain or TCP socket, instead of stdio if you like as well. Same for the qemu "monitor" interface.
Now, provided you have the sgabios.bin firmware, and that your VM doesn't use graphics (just VGA BIOS text output), you can also just use the -curses option:
kvm -hda yourdisk -curses
The VGA console is then shown in your terminal. If you need to access the qemu monitor, press Alt-2.
Best Answer
A look-like of the old Norton Commander in Unix is Midnight Commander. I have been using it for years, and in some situations it is particularly useful.
In Debian to install it, do:
To run it you call
Besides the familiar text graphical interface, in the bottom (command) line you can also perform shell commands.
Some functionalities are also associated to commands by default, and you can create new associations.
Midnight Commander also understands ssh/scp and one of the two text windows can be a remote one.
https://www.midnight-commander.org