Hey everyone, thanks for taking the time to help. In short, want to make sure I have the sub-floor properly spec'd... I removed old flooring (4 layers - 1 carpet, 3 wood) down to joists in most areas where feasible... there is some remaining 1 x 10 plank sub floor. I need to run the new 3/4 white oak parallel to the joists (yeah, I know) partly for aesthetic, but mostly how it will tie-in to other rest of the original hardwood areas. Fortunately, the additional layer discovered at tear-off will provide some room to add an additional layer to help stiffen the floor for parallel hardwood/joist installation. Please see attached PDF for a rough sketch.
1 - Can I use appropriate screws w/ adhesive to attach 3/4 CDX to joists (#10 GRK, etc.) or do I need to use a ring shank nail? If nail only, can I use clip head nails (I only have a framing nailer that shoots clip head nails.)

2- Adhesive between ⅜” and ¾” layers? Staple or screw 3/8 to 3/4? (e.g. Patriot Timber's Sureply states no adhesive, staple schedule only with their underlayment.)
[img]Floor%20Assembly.pdf[/img]
3 - Bridging good idea or bad? (see PDF)

4 - Sistering good idea or bad? (see PDF)

5 - Any general feedback on moisture meters? Will use primarily for wood projects. Although an occasional lath and plaster scan would be nice. Can you get anything decent for $200- $300?

6- Lastly what's your pref on adhesives for sub-floor? (Bostik, Titelbond, Liquid nails)

Any input is appreciated. Thanks!

Solid wood sub-floor will be stiffer than plywood. The screws will be more than sufficient for fastening the 3/4 plywood to the joists. If you have not already bought supplies, have you considered using one layer of inch and an eighth plywood? This will allow better fastener holding power for the 3/4 oak flooring instead of going through a 3/8 inch ply and partially embedding into the 3/4 inch sub-floor.
The framing for inch and an eighth ply sub-floor will be plenty of support. Block any butt-joints, but it is T&G on the edges. Fasten it with the screws on 12 inch centers across the joists, after you have checked and flattened the joists. This thickness of sub-floor will not need bridging to help support a load.
If you find a moisture meter in this price range it will be accurate. Harbor Freight has an inexpensive model that you could use to compare the new flooring to the moisture content of the old flooring, since you only like to have them the same reading.
I like use a latex based sub-floor adhesive by Titebond.