So my house has 2x6 car decking/tongue and groove/whatever-you-want-to-call-it subfloor that I am going to tile over, both in the kitchen and the bathroom. The rest of the floors are 3/4" oak as you can see in the pictures.
Underneath the subfloor is post and beam construction--4x8 beams about anywhere from 3-5' apart from one another (3' from the outside wall, then 5' thereafter). So the 2x6s span from 3-5 feet at a time.
There are two spots that I replaced some old rotted sections of the T&G which you'll notice in the pictures below. The older sections of subfloor were a bit springy in spots so I nailed some 2x4s flat from below, putting a nail into each piece of 2x6 along the way. This stiffened them up considerably and there's hardly any give to them anymore.
My question is how should I go about laying tile over this? I have the 3/4" wood floor to tie into so I don't want to go too crazy with additional underlayment.
From some initial research, it seems my best option might be to go with a layer of 1/2" plywood screwed to subfloor, then thinset/screw some 1/4" concrete backer, then thinset/tile. If I start with ply on the subfloor, do I need to use tar paper underneath that or should I use some self-leveler before laying down the ply (or do you do this on top of the plywood?).