Stupid reddit app won't let me hotlink anything in the body text for some reason, so check the comments for my links.

I'm remodeling a shower and need to know the difference between standard Hardie board and the water proof stuff. The water proof stuff is only like ten bucks more per sheet but apparently you don't need to coat it with anything. Just want to confirm this is true. I thought the only stuff you didn't need to coat was kerdi board. Also told you don't need to coat the joints if you use green alkali tape, is this also true? Also can't find green alkali tape at Lowes. I've got a green tape, but it's not alkali, and I've got an alkali tape but it's not green, lol.
For the screw holes, assuming the above is all true, I'm told you can just use a sealant caulk for them.

Thanks in advance.