We have a 25' FB AS that's 7,600lbs, 835 tongue. We tow with a 2017 Disco TD6. I have also towed it with a 2016 LR4 SCV6 and a 2014 RRSS (V8).
All three vehicles did a great job. The D5 has done the best.
1. Yes, we use weight distribution. The air-ride suspension does not mean you cannot use it. In fact if you look at Jeep Overland's and higher with air-ride they suggest you use weight distribution, which is a very US thing. Europe doesn't believe in weight distribution and also has trailers, like airstreams, that are made a little different lowering the tongue weights.
2. We have towed the AS with the D5 11k miles or so last summer without issue. It HAS to be set up properly. Meaning that we spend 3 hours getting the drop bar on the hitch just right so the AS was level and not pushing up or down on the air-ride.. This is where I agree with another poster about not using weight distribution.
3. Towing last summer we saw between 11mpg and 16mpg towing with the D5TD6. With the RRSS and the LR4 we saw 9-13mpg. The low end torque on the TD6 is unbelievable and between the three vehicles the "fun factor" when not driving is closer to the 500hp RRSS than the LR4.
My suggestion is that if you are going to use this for a tow vehicle get the TD6. The SCV6 will be fine but the TD6 is better. We have 35k on our 2017 (Dec 2017 delivery) and I couldn't be happier.
I have also thrown on BFG KO2s for that 11k trip and they rode great. Finally this D5 TD6 is the best vehicle I've owned and I'd consider myself an enthusiast (we currently have a fleet of 6 cars - all German or British). It's the perfect combo of utility, fun, and nice. Was looking at a TD6 Full Size but went with the Disco to get the seats that go flat for mtb and dog transport inside.
It's a great car and tows perfectly.