What config changes do I need to make so that LXDE doesn't start at
boot
This is probably a very late answer since you first posted the question. Anyway, from what I knew working on a similar situation on Ubuntu-based Linux OS using lightdm as display manager, you can use systemctl command to set the default boot into terminal mode after booting up.
First, you may want to check what the default mode is;
systemctl get-default
To change the default mode, and if you don't want the desktop environment to start at boot, shall do this;
systemctl set-default multi-user
On the next reboot, it won't show the greeter and user login by your display manager (lightdm in this case) and won't boot into your desktop environment but instead goes into terminal mode.
If you want to set default boot up to your desktop enviroment, you shall do;
systemctl set-default graphical
If you want to set default boot up to terminal without the desktop enviroment, you shall do;
systemctl set-default multi-user
And for this;
, but I can still jump into it with starts?
From the terminal;
systemctl start lightdm
Or by using SysV init run level;
init 5
It will start the display manager and runs your desktop greeter and login session before loading into your desktop environment. This will run even if you have the configuration set as multi-user previously. But, when you reboot the next session, it will go into the default mode set previously.