First, I'd like to say that I am a big fan of TOH and subscride to the magazine. I own an old farm house built in 1889.
I am planning to remodel my kitchen. The room will be 13.5 ft by 26 ft. The floor joists are 2"x 8" rough cut, 16" on center with a 13.5 ft span. The space below the joists is on average 3" with dirt below(not much of a crawl space). My plan is to reinforce the joists by glueing and nailing 5/8" plywood strips on one side of each joist, and place two rows of blocking(bridging) evenly spaced. I then plan to insulate with fiberglass batt (R19) resting on foam board insulation attached between each joist space. The sub-floor will be two layers of 5/8" plywood staggered and offset to ensure no joints fall on top of each other. The finish floor will be either 12" or 16" tile. I want to heat the space with radiant floor heat. I have purchased an outdoor wood furnace(Central Boiler) as a secondary heat source for the house with an oil-fired furnace(forced-air) as the primary heat source.

The plan for heating the floor is to attach 30 lb tar paper on the sub-floor, run two circuits of 1/2" pex tubing, and float a mortar bed approx. 1" thick over the entire floor as a base for the tile.

I'd like to know if this is a sound plan and if I am missing any important steps. I believe I should be installing wire mesh in the mortar bed but it would have to go on top of the pex. Then, it would be difficult to use screed strips for floating the mortar bed.

Can I lay the bed in two lifts with the wire mesh in the second lift?

Digging out below the floor joists in order to install the pex and insulation is my very last option, again there is only 2" to 3" inch space below the joists.

Any input or assistance would be greatly appreciated.