=====Starting X=====

 There's a bunch of things that get done by DE's under the covers that you need to straighten out when you're just using a WM like i3 or fluxbox etc. Things like dbus and wallets. These need some attention in the way the WM is started up but I like to do it the old fashioned way - that is explicitly, without relying on bonnet-welded-shut, secret-propriety, dont-scare-the-horses, patronising-we'll take-care-of-you bulldust. Once you've got the startup covered, it's a simple matter of selecting the tools you like. I'll post separately on how I deal with my laptop quirks (detecting and acting on lid, brightness, etc) 

Firstly it depends how you login.

If logging in to a system console and then running 'startx' (or if coming in from VNC) I put this in ~/.xinitrc:

  #!/usr/bin/env bash
  # This is called by xinit (or startx or Xvnc). It should set up 
  # everything that is set up by xdm etc.
  
  ERRFILE="$HOME/.xsession-errors$DISPLAY"
  exec &> $ERRFILE
  set -x
  XSESSION="$HOME/.xsession"
  
  LAUNCHER="dbus-launch" # should maybe use /usr/libexec/at-spi-bus-launcher like lxdm does - but it's only for accessibility ie screen readers etc
  if type $LAUNCHER &> /dev/null; then
      LAUNCHER+=" --sh-syntax --exit-with-session"
  else
      LAUNCHER=exec
  fi
  
  [ -r "$XSESSION" ] && {
      chmod +x "$XSESSION"
      $LAUNCHER "$XSESSION"
      exit 0
  }

... so that gets me (hopefully) to the same point that xdm/gxm/kdm/lxdm whatever would do. 

Logging in from xdm/gdm etc:

I put this into /usr/share/xsessions/xsession.desktop so that the login manager gives me an 'xsession' option as well as whatever DE I have installed:

  [Desktop Entry]
  Encoding=UTF-8
  Name=XSession
  Comment=This session will run your ~/.xsession
  Exec=$HOME/.xsession
  Icon=
  Type=Application
  
  [Window Manager]
  SessionManaged=true

I have this in ~/.config/desktop so I that .xsession starts the right one:

  WM=i3
  # WM=startfluxbox
  # WM=starte16
  # WM=enlightenment_start # e17
  # WM=gnome-session
  # WM=startkde
  # WM=fvwm2
  # WM=icewm-session
  # WM=twm
  # WM=dwm-start
  # WM=awesome
 
Now for ~/.xsession: {{startup:xsession}}

The final piece is to tell VNC what to do: ~/.vnc/xsession:

  #!/bin/sh
  #vncconfig -iconic &
  
  WM=i3
  #WM=startfluxbox
  #WM=starte16
  #WM=enlightenment_start # e17
  #WM=gnome-session
  #WM=mate-session
  #WM=startkde
  #WM=fvwm2
  #WM=icewm-session
  #WM=twm
  #WM=dwm-start
  #WM=awesome
  export WM
  
  # some remote vnc sessions were seeing this set to an invalid value
  # (maybe it was for the local system rather than the remote!).
  unset SSH_AUTH_SOCK
  
  XINITRC=$HOME/.xinitrc
  [ -r "$XINITRC" ] && {
      chmod +x "$XINITRC"
      exec "$XINITRC"
  }