All of our strongholds/environments AND our world map were created in the same editor that will ship with the game.
The only thing that would limit 'continent creation' is that if you make a truly huge map, you will run into some lag, just like in any other game. But large environment and Civilization-esque continent maps are perfectly feasible.
Plugins For importing/exporting from programs like 3ds max and maya
No plugins required.
Easy crowed creation unlike AOM
If you meant 'crowd,' then this is another yes. Units can be placed either individually or in battalions (usually of 10-15 units). So massive armies can be created with a relatively few number of battalion markers. Alternatively, using the editor's "Copy/Paste" tool, you can select to copy a square of units while not picking up any of the terrain/elevation/water/etc, and paste the units to create a large, if not repetitive, crowd.
Unit stats can be changed without any knowledge of triggers or scripting. And we have a lot of stats you can play with including height, width, length, opacity, hover, speed, LOS, etc. as well as dozens of attributes that can be modified on FXs to create an entirely new effect. All without triggers/scripting.
A bit more complicated, but if you're familiar with the Lua script language, this should be very doable. If you just want to change the graphical backgrounds on the UI, you can do this simply by overwriting the appropriate images. You may also be happy to know that DOF's textures don't deal in any obscure formats like AOM's .ddt. We use .dds, which can be read with programs like Photoshop and Paint.NET with no plug-ins required (although, last I checked, Gimp does require a simple plug-in to read this format).
You can make both single-player and multi-player scenarios and campaigns. I'm not too familiar with the Total War gameplay, so you'll have to elaborate before I can make a comparison.