I like the idea of a demi-lancer, seems to fit the empire theme (anno 1600).
My setup for a demi-lancer would be:
stats: WS 4, I 4, LD 7, 2 A for champion
Full plate armor, unbarded horse and a lance.
special rules:
Precision strike+1 to hit on charge, using no shield gives the lancer a better aim.
Couragous chargeImmune to psychology on the charge
18 pts per Demi-lancer
I think a full plate would fit the Demi-lancer very well:
link to wikiDemi-lancers used mostly half-plate armor which is imo full plate in warhammer.
Also a 3+ save would make them able to take some fire but not enough to replace true knights. And with ld 7 they are not really reliable to stick in combat.