Building on top of 3/4'' plywood subfloor
The 3/4 sub sub floor is sufficient.

I have some comments about Redguard on the shower floor.  

While the product (and others like it) is rated for a directly-under-the-tile waterproofing, I have some cautions (directed at the installation in the DIY blog article) :

Be sure you do a minimum of 2 coats, at right angles (as recommended).  Be sure you lightly hone the cement base with a rubbing block, for a bump-free surface, before coating.  If you have any voids, fill them in with the thinset you will use, before coating (using a portland cement thinset, not a premixed mastic thinset)

Be aware that the unprotected Redguard IS NOT abrasion, scuff or scratch resistant.  A dropped tool or tile will cut it.  Be very careful walking and kneeling on it.. 

Consider using a sheet membrane product (Kerdi, NobleSeal TS) for the floor and using Redguard on the walls only.  I would put the Redguard at least 4ft high on the walls or a foot higher than wherever the direct spray would hit the wall opposite the spray head (whichever is higher).