The only vehicles he can possibly bring are Soul Grinders, so you don't really need a dark lance heavy list - swap out dark lances for disintegrators on more stuff, give every Venom the second splinter cannon, don't waste points on Incubi, agonisers or other power weapons as their daemonic saves are all invulnerable anyway. I'd favour warriors over wyches in this instance because of the volume of fire and the points saving. I'd still take some wyches, because they're quite good for holding stuff up - if you can ground the daemon prince, you can do what I did recently - charge it with wyches, and stop it zooming around for as long as possible. Two units of five or one of ten with shardnets would maybe be even better for this, as mine were basic and just took a wound off it over two rounds of combat, leaving a Venom to finish the job. Wracks could be a good bet if you take a haemonculus, as they'll be better for holding objectives, and poisoned weapons are what you want to be bringing.
Essentialy, take the basic stuff and give it the highest volume of shots that you possibly can - spam splinter cannons and disintegrators, maybe take a Razorwing to play with the flying monsters. Mount everything in vehicles. Maybe take Reavers with cluster caltrops, as AP- isn't an issue against all those invulnerable saves, and they can hit those flying monsters automatically with their bladevane attack.
After the first wave come in, don't be afraid to completely redeploy using your speed. If you sit still to unload everything into him, whatever is left (and there's a good chance there'll still be stuff left, with it all being fearless) will still be able to potentially wreck your stuff. And if you sit still, the rest of the army drops in and it's all together in one massive, gribbly wall of nastiness, hitting you without you getting a flat out cover save. If you move all of your stuff out of the way of the initial wave, at least you can deal with his army piece by piece, rather than trying to take it all on at once (unless he deliberately deep strikes all his units a long way away from each other, but looking at his list of multiple small units, this doesn't look like a smart move on his part).
Divide and conquer!