The MXT is a really great detector. I too, learned on a White's 6000D back in the 80's. Graduated to an XLT then XL Pro and just last year to the MXT (after hearing so much how good it is). The MXT is the deepest out of all of them. Better still, it's the easiest to use and most forgiving too. Coming from those old White's analog machines, the transition will be easy.
A couple things you'll notice about the MXT compared to the older analog detectors. First, it is chattier. This is both a function of the SAT speed being faster and the MXT using fewer filters. The chattiness doesn't hurt the performance at al, and in fact probably helps it be a little more sensitive. If the noise bothers you, you can just hunt in normal relic mode which quiets it way back down to be more like the old analog audio you are familiar with.
Second, the sweep speed is much more forgiving on the MXT. On the old 6000D's (and XLT and XL Pro) you had to really whip it to get the best depth. As you slowed down, you'd lose depth but gain separation. It was always a big tradeoff between depth and separation, and when you got too slow, the detector would basically stop working altogether. Not so on the MXT. It tolerates a much wider range of sweep speeds. You can go fast like the old detectors, but you can also slow way down and still get good depth AND get great separation. On top of this, the recovery speed is much faster too. When I transitioned t the MXT, the hardest thing was to learn to slow down when in the trash ... and that you can actually effectively hunt in heavy trash!
For coils, I'd suggest starting with the best all-around coil for the MXT (in my opinion): the White's 6x10 DD. Sure there are other coils that go deeper, and other coils that do better in really heavy trash, but the 6x10 does it all reasonably well and covers the widest range of conditions you're likely to encounter. It separates really well for its size, and when you get into the really heavy stuff, you can turn the sensitivity way down and effectively have a smaller coil.
Good pick on the MXT! I never thought I could ever move away from the older White's analog detectors that I loved, but I have finally found an alterative that really clicks with me .. the MXT. You should really like the MXT too. Good luck and let us know how it's going.