Vim and custom functions

My personal vimrc and custom funcitons for daily use

What I use as my plugins?

Plug '~/.vim/plugged/custom-functions'
Plug 'vimwiki/vimwiki'
Plug 'majutsushi/tagbar'

yes, the custom functions file must be initialized and installed like a plugin
Nope, no autocomplete here.

Todo

1. Make a function to verify if the customfunctions.vim exist or not in the right place
2. [thinking on...]

About the number 1

I know, I know, it's easy to make a function to do that, but I'm trying to study differents commands on vim and maybe a better way to do the 'common'.
I'm not trying to 'reinvent the wheel', I'm just trying to learn more!!