Dietra/Subfloor/Porcelain or Ceramic?

I'm remodeling an existing 18yr. Old kitchen.
The existing floor is a thin vinyl sheet goods glued on an underlayment of 1/2" luan plywood screwed and glued over a sub-floor of 17/32" T&G plywood. Joists are 16"O.C. Yet the subfloor/luan has a half-dozen or so squeaks. I'm suspecting delamination of the luan is causing the squeaky areas which are up to 2'square.

Also, a 4'x8' area of the old floor has diagonally settled up to 7/16"very gradually into a corner pantry which is the lowest spot. Is there a satisfactory self leveling cement fix or must I replace joists and subfloor?

I also understand that Dietra is an excellent base system to use in this application after eliminating the sub-floor squeaks by rescrewing w/2-5/8" decking screws 24"OC directly through all of the old floor into the joists. Is this a realistic fix and will decking screws hold satisfactorily under the Dietra if the heads are slightly countersunk?

Using Dietra, I'm told the new tile floor could be either porcelain or ceramic which provides a wider selection and possibly less cost, however, I was initially focused on porcelain at a much higher cost due to it being harder and perhaps less inclined to crack. Are there any other advantages/disadvantages to consider in the selection of tile? And, should a modified grout be used with the new tile for some flex?

Thanks,

Bill

I am not an expert, but I do have a copy of the TCNA handbook!
This is a handbook of accepted minimums for tile installations. There is a deflection calculator on another site (john Bridge or the Floor Pro Community, I cant remember)
That will help with the structural issues. As far as I know, the minimum thickness of a stone or tile floor is 1-1/4" with a minimum flex, or deflection allowed depending on tile or stone. Also, porcelain does require a modified thinset, not so much for flex, but for stickiness as the porcelain is so smooth grained. You may need to sister the joists and either add to, and/or replace the subfloor.
As for Dietra, I have heard nothing but praise, and if countersinking screws, that should be fine as Deitra is adhered with thinset anyway.
This should get you started anyway!
Any Pros care to chime in?