From your question it appears that you have installed vim-tiny 8.0 that is a very minimal Vim runtime without plugins. You can confirm this using this:
dpkg -l | grep vim
You can have several Vim runtimes, but the version running when you do
vim will be the version that you can see indicated here:
update-alternatives --list vim
You can check other versions. My suggestion is that you decide between full versions with support for GUI, and you can choose between
vim-gtk2/vim-gtk3 packages or
vim-nox that is a full version, but without a GUI.
Now, IIRC, the Vim full version in Debian/Ubuntu doesn't come with Python 2 AND Python 3 at the same time in 7.x versions. I don't know how the case is with Vim 8, because I use
neovim now. If this is the case for you and you are going to need BOTH Python engines supported by Vim 8 (this will not be your case for use
YouCompleteMe; this one works with Python 2 support only) then you will need to compile from sources your own Vim 8.0.