Hey Matt,
For your age and being your first dio I think you have done a great job.
Also welcome to Armorama,if you like models and dios there's not a better place to learn and get advise.There's a lot of info to gather over a long period of time to do amazing dios.My first suggestion to you to work on and it will be a little time consuming is to carefully cut the bases of your figures and then glue them.A dio should be as close to real life as it can be and nobody has a platform under them.
You'll find info overload as you go on so I'll just leave you with that to start.
Keep up the great work and keep us posted on your progress.
To see what years of learning can do,scroll down to"That Aussie's in Iraq Diorama, 2006'.