There are plenty of mods available already.

Two of the best sites for these are AOC Curse Addons and Conan Mods.

The mods I'm personally using are:

• Mirage UI - Improved group window and more hotbuttons (godsend for melee) and available in different sizes (I use 3 button small)
• Compact Region Map - Saves precious screen real estate by removing the border around the map
• Cedes Combo Sequence Indicator - Shows you which key to press.

Here is a screenshot of my current setup using the above mods:

Download full version