About the Fungi Biome, I suggest waiting until your next one, The Tropics is out, considering this; In Terraria, the Mushroom Biome is Mushroom Grass on Mud, and it requires Mud to work, The Tropics will be a Jungle Equivelent, and therefore, will likely change mud into another block, the block that replaces Mud should be taken into consideration should a Mushroom Biome Alt be created, unless of course, you want them to be completely seperate, as this suggests that both The Tropics and the Mushroom Alt would be together as one package, but you said yourself, that they are standalone suggestions. So it might just have to work on normal Mud anyway.
Doesn't really look like you've thought about a Mushroom Alt until now, but admittedly, thats not a bad idea.
Just please for the love of God change the music, I rather dislike the Mushroom Biome's current music XP