Playing the elves for the first time and learning a lot about what they can and cannot build...
I really like the idea of having them ride deer vs. horses, but...
It gets a little confusing.
You need horses to build a stable so you can build Elven Horsemen.
Then, after you research Stirrups, you need deer so you can build Fyndwell.
The Civlopedia doesn't say you ALSO need horses or you cannot build the stables. This doesn't make much sense IMO if the little guys are going to be riding deer vs. horses.
My suggestion would be, if it can be done, to eliminate the requirement to have the Horse resource and replace it with Deer for the Elves. Then, all the units could be 'deer-driven' instead of some riding horses. Or at least for the Fyndwell don't have the Horse resource requirement for stables when you need Deer.
Possible?
I think a great job has been done showing which units are buildable by which civs so you don't waste your time researching certain techs. For example, I love to get the Berserkers, but seeing there could not be an Elf Berserker, I went for other techs.
Nice work!