Home-manager neovim plugin config problems

I’m having some problems currently with neovim being configured via home-manager.

Specifically I can’t seem to do some function calls which should(?) exist.

Here is my neovim value:

  enable = true;
  vimAlias = true;
  vimdiffAlias = true;
  withPython3 = true;
  plugins = with pkgs.vimPlugins; [
      plugin = vimtex;
      config = ''
        let g:tex_flavor='latex'
        let g:vimtex_view_method='okular'
        let g:vimtex_quickfix_mod=0
        set conceallevel=1
        let g:tex_conceal='abdmg'
      plugin = deoplete-nvim;
      config = ''
        let g:deoplete#enable_at_startup = 1
        call deoplete#custom#var('omni', 'input_patterns', {
          \ 'tex': g:vimtex#re#deoplete
      plugin = ultisnips;
      config = ''
        let g:UltiSnipsExpandTrigger = '<tab>'
        let g:UltiSnipsJumpForwardTrigger = '<tab>'
        let g:UltiSnipsJumpBackwardTrigger = '<s-tab>'

        snippet beg "begin{} / end{}" bA
  extraConfig = ''
    setlocal spell
    set spelllang=en_gb
    inoremap <C-l> <c-g>u<Esc>[s1z=`]a<c-g>u

The error I’m getting:

Error detected while processing /nix/store/1574brxklmsh2j1h3ra711fqjg68pn3v-vimrc:
line   27:
E492: Not an editor command: vimtex#init()
line   31:
E121: Undefined variable: g:vimtex#re#deoplete
E116: Invalid arguments for function deoplete#custom#var
line   40:
E492: Not an editor command: snippet beg "begin{} / end{}" bAbegin{$1}
line   42:
E481: No range allowed:   $0end{$1}
line   43:
E492: Not an editor command: endsnippet

Afaict the plugins aren’t loaded when these lines are executed, thus the functions don’t exist, however I can’t figure out how to confirm this if it is true…

Any help would be appreciated and also hopefully serve as some decent documentation on this issue.