When we made dominions we didn't intend to make 1000+ units and hundreds of spells. At first I had perhaps five spells planned for each magic path and there were no schools at all. Our first step was to make a battle field where you could move a single soldier and have him strike an opponent. Then some more soldiers followed. Then soldiers were bereft the freedom of will and squads and commandrs were introduced. Then came orders other than move/attack. Still no spells. Then some strategic level with a map. Then some magic research, but the research system was remade several times until it became what it is today. By that time we had more than a hundred spells, but still not what we have today.
Try to start with some basic things. Huge lists can wait. It's very easy and fun to add new stuff when you have a system that works.
Your first priority should probably be to make something that you can 'play'. First of all just an '@' that moves around. Then a way to fight monsters and a monster to fight. Then some magic perhaps. Then more world to move around in. Etc.
This worked for us anyway. If we would have started with a list of 1000 units and spells we would have given up sometimes during 1997
