This looks great! I hope it will live up. I have just few questions:
1. Will Great war be fought in Skyrim or in Cyrodill?
2. Will Redguards of Hammerfell have presence?
3. Will it story be effected somehow if Emperor is killed?
4. Will mod be able to install middgame?
EDIT: If I may recommand, add some Orcs to Imperial ranks too.
2. Yes, somewhat
3. Not really
4. It should work fine, but it's always best to start a new game with anything this big.
Once in a while you should see an Orc or two in the Imperial ranks.
Will it be possible to play as an imperial loyalist against the dominion?
If you play as an Imperial in the Civil War, yes.