The complete consolidated facilities mod package is highly recommended. It populates the airfields and includes well-modelled versions of many famous aerodromes. It also includes the Vauban fortresses at Lille and around Verdun, plus Havrincourt Wood (commonly referred to as Mossy Face Wood). Be sure you have downloaded the complete OBD skins package from the Woff website. There are other skin packages available on the main mod website (link on Woff website). You may be interested in the version 6.5 add-on flight model pack by VonS. While he has included some fairly rare variants, some of his models help to keep things historical. For example, early RFC Spad 7s were the 150 horsepower models, while the vanilla version in the sim is the 180 horsepower model. This mod package allows you to tweak things accordingly. It's creator has a thread on the forum about which models to use when for the historical DiD campaigns that you will find helpful.

As an absolute must, download the collection of maps made by RAF_Louvert. They show the landscape the way it appears in the game and allow you to navigate properly from the map without needing the big fuzzy in-game map. They also include more accurate names for towns and villages that appear in the game.

The news mod will update the newspapers that appear in game and will add more historical events.

Good luck!