No. Just no.
1) The syntax here is ridiculous. "Instead of just adding 1 mana" is Unglued-material.
2) There is no reason to give them new land types. I guess that you were going for something like an upgrade-scaling (peak > mountain, jungle > forest etc) but it has no purpose; Cards referring to mountains won't react to peaks and you'd have to make future cards like " target mountain or peak" which is just unnecessary.
3) The whole idea of a land giving five mana is just... WEIRD. Not to mention it's imbalanced, even if you make the lands are legendary. You'd be able to go for a turn one Deus of calamity! Show me ONE player who could protect himself against something like this from turn 1 on!
Here are some alternatives:
- Reduce the given mana to {3}
- Add some drawback, like it has to enter the battlefield tapped, you have to control a land that shares a type with it, or maybe you have to sacrifice it if you don't control any permanents of it's color etc
Maybe even go back to the champion-mechanic (like, "Champion a mountain" for the Giant Peak?)
-Give the cards their respective landtype