3'x5'x0.5" durock is 35 pounds with 30 year warranty rated for interior/ exterior. Hardiebacker is slightly heavier with a limited lifetime warranty rated for interior. Just in case you go to store and see both, durock should technically hold up better and last longer due to the glass fibers, which also make it messier. Anyways durock comes out to about 2.3 pounds per sqft. So about 75 pounds for a 4x8. If you're doing a backsplash usually 3x5 will work. 4x8 if doing a surround. 75 pounds isn't terrible, but it's an inconvenient shape to man handle, as it's semi floppy at half inch, and extra floppy at 1/4, depending how you hold. Regular Half inch drywall is a little under 60 pounds for comparison. More on reddit.com

I usually use 1/2" Hardiebacker over bare studs, screwed with 1-5/8" Backer-On screws. I tape all flat and corner joints with any thinset and heavy-duty mesh tape like the Durock brand. I usually plan my drywall/backer board vertical seams so the tile will just run onto the drywall, and I don't tape this joint (whether bullnose or Schluter trim, it's beyond the glass or curtain line - if it's getting wet, you have other problems). I use any old thinset, since it can get oxygen from the back, there's no issue with curing. It's not necessary to spot your screws with thinset. Redgard or Aquadefense. I install plastic niches before the board goes up and use a little Kerdi tape over the lip. TBH, I prefer to custom-make them now, as I don't particularly trust silicone's bond to the board (perhaps removing the niche after boarding and sealing the board edge would improve the bond here?). Custom-sizing allows for fewer layout issues, as long as the job allows some leeway in size/location. I've been doing showers with mud pans only, no installs over acrylic pans or tub bases. I'd probably keep the board off the flange, prefill and then embed tape over the transition. More on reddit.com

You can use either. The waterprooofing is the important part; none of the board choices are waterproof. You can use a paint-on waterproofing like redguard; I prefer a membrane like Kerdi. More on reddit.com

We've diy'ed a lot of apartments bath remodels (approx 10). Before we wouldn't waterproof over cement board. My dad helped us tile and that just wasn't a thing. Most were tile around tubs. We did a lot of research when putting in a shower pan and now use the paint on water proofer in all future projects. Also please dear God don't let them grout the corners, should be silicone matching the grout. More on reddit.com