The one annoying thing about the Blacktips that I've noticed are that no two are weighted the exactly same. You will probably need to tweak things a little bit to your liking. I would just check to see how it trims out as stock first and also check the weighting on the nose cone.
Two DeWalt (9Ah / 12Ah) batteries weigh around ~1460 grams each. (~2920 grams total)
The salt water plate inside the body should stay in the tech tube. You only need to remove it if you're diving fresh water. My nose cone is weighted to be around ~2635grams. I've seen them weighted anywhere from ~2625-2690 grams You can use a food or postage scale to help check this. Keep in mind anything you add to the body needs to be accounted for including a medium bolt snap on the nose.
I personally prefer my scooter to be slightly buoyant / neutral at depth since I find negative scooters annoying. There is some minor amount of o-ring compression that occurs at the tail and nose section. This means that if your scooter is just a hair positive on the surface it will likely be neutral or even slightly negative at depth as the o-ring seals compress.