Hi Tay -
I appreciate your excitement about portraying a medical unit and the Evac Hospital would certainly be respectable, but I agree with Dirk that it would be a huge effort. If you look at personnel alone, the Semi-Mobile Evac Hospital had a staff of nearly 300, 400 beds and had a minimum footprint of 150yd by 150yd. Once you start looking at the different tents and equipment it doesn't take long to realize the size of the project. Of course you could setup just the triage or one ward, but that is still quite a large display.
For me, the Battalion Aid Station is the easiest to assemble and display. The BAS would have been setup within a couple hundred yards of the front line and would have taken advantage of whatever terrian or feature was available - tent, root celler, dugout, empty field, etc. And technically you should be able to transport in a couple jeeps with trailers.
Having said that, other options might include part of a field hospital. Field hospitals can be task organized into smaller self sufficient Clearing Platoons. Each platoon would have about 100 bed capacity and staff of about 50. Another aspect of the Field Hospital is that the WC54 was part of the organic equipment. These platoons would have been more flexible in where they operated and certainly would have less of a foot print. The Portable Surgical Units were extremely flexible units that sometimes operated independently and sometimes augmented other units. Its staffing was less than 40 people and had less than 1000 lbs of equipment that could be man portable.
As for where to start, get a copy of the Medical Soldier's handbook. This will give you a basic understanding of military medical care, equipment and structure. As I'm sure you are aware the medical field is extremely technical and its much more difficult for those of us that are typically patients to discuss military medicine with others that are medical professionals. If you ever have a chance to attend one of Dirk's displays, you will see the difference of someone who knows what they are talking about versus me who can't even play a medical prefoessional on TV
And don't forget to look here for more infomation about different medical units http://www.med-dept.com/org.php
Good luck and let us know what you decide.