I haven't played Empire since Wood Elves, but it's definitely one of those factions where you'll often have to restart to get a favourable diplomatic layout. Keep your eastern neighbours placated -- they're typically your best friends, good trade partners, and a good barrier against VCs.

North is hit and miss. Some games they hate you, others they don't.

West is Marienburg, who if you're lucky will go to war with Bretonnia. When that happens, join the war, kill Marienburg and take their capital (it's an insanely strong money maker). That'll hopefully buy you some favour with the Bretonnian factions, which you can use to build alliances, which will help keep the WEs at bay.

Your goal by turn ~120 is to have a really strong barrier against the North. Guard against ships with Marienburg. A single general + cheap army of spears and crossbows is plenty here. Empire factions to your north will provide a good buffer against initial Chaos push, plus fertile lands for you to resettle once they get obliterated.

At this point you basically need to decide what's the bigger threat -- chaos or WEs, and eliminate them. Utilise your greatest strengths (artillery, magic, cavalry). Each of your main armies should have a battle priest for replenishment, a wizard, and a witch hunter hanging around (not embedded) for army blocking.

The biggest key for me in Empire Legendary though was just accepting that I'd need to restart a few times until the political landscape was tenable.