I think my virtual machines left about 1-2gb for the swap partition. When I did it I think I followed the same rules as for the Windows page file, 1.5x-2x RAM and I have my VMs set to use 768mb of RAM.
My rule for swap is RAM + 1 GB that way I am guaranteed no trouble, even with hibernation.
Good call. I was going to set it to 1GB, but now you mention hibernation...
I generally give between 10 and 15 GiB, which is more than enough. My current install on my laptop is 12.5 GiB for / IIRC, of which I think I am using around half.
Ok. I will go with 20. I think. I tend to install a lot of development libraries so I think 20ish should be what I want.
Then I always encrypt /home, just because I <3 encrypted personal data.
I expected nothing less from you

I am moving from Ubuntu to Arch, as I really dislike Ubuntu's update method. Rolling release is the way forward in my opinion. Also in separating / and /home I can always move back if I dislike Arch more.