There is a complete list of the unit traits and abilities which you can find in the game directory. Go to the install directory (probably C:\Program Files (x86)\Steam\SteamApps\Common\FE LegendaryHeroes, if you installed in the default location), go into the Data\English directory, and find CoreAbilities.XML. All traits used for unit design are in that file, which gives the trait name displayed in the game, an internal name used by the game for that trait, the production cost (if any) for the trait, whether or not it can be used for unit design, whether the trait is a level-bonus for champions, and what prerequisites the trait has. The various blood bonuses and the faction traits are also in this file.
Unit abilities can be found in CoreSpells.XML, found in the same directory as CoreAbilities. Once again, the abilities list the name displayed in the game and an internal name used by the game. Any costs for using the ability are included, as are its effects and the in-game description for the ability. If there is a prerequisite for using the ability, that will also be listed in CoreSpells.
These things may at some point go onto the wiki that some people have begun to create.
Also, is there a way to get enemy unit stats / details of a specific unit during tactical battles?
I believe that the Unit Details screen will be brought up if you double-click the unit (or its portrait) during a tactical battle. Might also be done by right-clicking the unit or its portrait, I don't remember at the moment.
