I am new to plumbing and was given the 3 rules as follows:

1) Excrement runs downhill (at a 1/4" over 12" to 1/2" over 12" only)
2) Don't chew your fingernails
3) Use the sandwich bag to hold the sandwich by a corner while eating and feed the remainder to the family dog

With that being the extent of my plumbing knowlege, I am trying to build a support frame for a Jacuzzi soaker tub. The tub was sold as self leveling and has some rather large blocks of foam glued to the bottom. I've heard of setting a tub in mortar (this one is acrylic) for bottom support. I have two questions,

1) Do I need to set the bottom of the self leveling tub in mortar?
2) How much shorter do I need to build the tub deck (this is a drop in installation) than the dry tub lip height? Basically, when I put it in mount position and fill it with water, how much is that foam on the bottom going to compress?

I don't want to build the deck too high (and will already be redoing the walls as the tub showed up 5/8" shorter than the spec print) and have the tub sitting on the edges and I'm worried that if I build too low the foam will not compress enough and I'll be redoing the entire thing.

Any ideas about these tub base types?