@Loatman Glad you liked the guide. Hopefully we can resolve this issue with startx; I've run through the installation instructions at least four times, using three different recent versions of Raspbian Jessie on a Pi 3; it'd be good to work out what the issue is.
The clue may be in you saying you don't have an 'exit to command line' option.
It's a little confusing as you seem to have the system configured to boot directly to the console, which happens when you use the Raspberry Pi Configuration tool (Raspian desktop, Menu, Preferences) to select Boot to: CLI. Setting this option is also what adds 'exit to command line' to the Shutdown menu in Raspbian.
Did you set your system to boot to the command line in some other way?
Just to clarify, is the prompt where you type startx the main console - e.g. does you Pi boot, scrolling a few pages of status messages, and leave you with a full-screen command line?
When you run startx what happens? Do you get an error message?
Did you use the option to resize the filesystem (assuming you weren't using the latest Raspbian image, which seems to run this automatically now)?
You can check the amount of free disk space from the command line with:
df -k
Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 61271084 36856840 21869428 63% / devtmpfs 437064 0 437064 0% /dev tmpfs 441400 67696 373704 16% /dev/shm tmpfs 441400 6268 435132 2% /run tmpfs 5120 4 5116 1% /run/lock tmpfs 441400 0 441400 0% /sys/fs/cgroup /dev/mmcblk0p1 61384 20960 40424 35% /boot tmpfs 88280 8 88272 1% /run/user/1000My system has a 64GB SD Card. In the above example, the main partition dev/root is showing a total of 61271084 1k blocks; divide this by 1048576 to obtain 58.43GB total, of which 63% is used
Btw: apologies for the delay in responding, I didn't have 'watch' set on the thread.