Is this a viable way to get the effect of Sun Worshiper to replace it with? Or is it being instant effect too direct? Currently Sun Worshiper is competing for a slot and this is one way to resolve the issue.

This seems ok, but it might be a bit pushed. The only card I can think that's similiar to this off the top of my head is Battle Hymn which was an instant but creatures and lands are two very different things.

Yea, the fact that lands don't cost anything is the main relevant diff. Though Discovery is more restrictive than landfall in that it's more specific and you may have to work toward increasing it to optimize some of the effects/abilities based on it. So this isn't quite as good as if it just counted all lands you control. It might be a little more powerful than battle hymn simply because it's a little easier to play a land with a diff name than cast a creature, but both cards likely don't start to achieve their full effect within the first 3 turns without manipulation to get more creatures or lands. The nature of a card like this tends to actually be weak as an early game card and strong in the mid to late game.

That's a pretty good card. Needs support to really shine, which is totally ok. Most likely extremely hit and miss in Limited, but that's the fun of it.

Sun Worshipper is pretty cool too, although sacrifice is not a theme in red. Could be a black card though.