I'd just use the lamp. Guineas aren't very smart birds and I'd be worried about losing some. You'd also need at least several pads for that many chicks, especially as they grow.
Having the lamp doesn't really contribute to pasty butt either, overheating does but you'll know if they're too hot.
Put some ACV in their water. ACV isn't a cure all like some say, but it really helps get rid of the pasty butt. I got rid of it in all thirty keets of mine in two days.
Wash the poop off of their bottoms, so they're not blocked up. And put a splash of ACV in the water. That should help if they're still having issues.
They're beautiful babies, congrats!