Sony TTS 8000 w Sony PUA 1600L

Lohanimal,
Here are my thoughts:
(1) Choose tonearm to match cartridge. Just about any tonearm will work on the TTS8000, except before purchasing a 12-incher you might check to be sure it fits the armboard.
(2) See my response to (1)
(3) Wood vs slate vs Panzerholz (which is a kind of wood, after all). These materials can all give excellent results if the plinth is otherwise properly designed and engineered. I personally have found that a combo of slate and a hardwood (cherry, not Panzerholz) is the most neutral I've ever heard, but in fairness, I have never "heard" a Panzerholz plinth.

You're very courageous if you are going to make the plinth from raw wood planks. I created an engineering drawing of what I wanted and gave it to a "real" carpenter, who made the base for me out of solid cherry. (Sounds like you yourself have some real carpentry skills; I do not.)

I then mated that base to a slate plinth that I had previously commissioned. I bought the slate slab in PA, had it cut and honed by the company that sold the slate to me. They then shipped the slab to a water-jet company, also in PA, where the slate was cut to accept the chassis of my SP10 Mk3. The slate slab and the wood base are held together by 6 or 7 large bolts that engage threaded inserts I installed into the bottom side of the slate. Then the Mk3 chassis is bolted through both layers, top to bottom. The slate alone was "very good", but I think the slate + cherry is even more neutral. (What else would one say after so much time, effort, and aggravation?)