We have a number of Ad revolving on the site, but sometimes when I upload them they don't show up?
They're sized right and in the right placement,
I'm using GIF's and they're a little big in size.
It looks like you have size restrictions set on your Zone and that many of your ads don't fit based on the rules that you've set on the Zone. It also looks like you need to target your Placements to a Zone. If you are using Ads, Placements and Zones; then typically you would have your targeting like this: Ad > Placement > Zone. So every Ad should target at least one Placement and every Placement should target at least one Zone.
Once you configure things like this, you may need to update your Ad Tags or Widgets to include the Zone machine name of the Zone that you want to serve.