1. There was a quality drive at the GC assembly plant in sept 2013, so build dates after this are the way to go. The MY14s (8 speeds) began production early 2013. Not seeing a lot of DPF issues, there are dpf cleaning products that some like to use. A catch can may be worth while. There have been some main bearing failures in the diesels, particularly when towing. Jeep made some changes to shift points and oil viscosity to address this. Haven't been hearing much of these lately, but they happen.
2. I haven't driven the petrol, but a lot of petrol owners on the forums and facebook pages seem happy with them. Something that is noticeable in the diesel (may also affect the petrol) is a bit of lag off the line or when rolling to an intersection and then getting on the power. It can take it a second or two to grab a gear and go, some have used iDrive units with some improvement.
3. Nothing obvious, most common issue going around is alternator failures (jeep is doing a recall on the petrol alternator, but not the diesel alternator). Aircon condenser cracking, get an aftermarket replacement if you get this. ELSD motor failure ont eh rear diff pops up now and then. Overlands have leather covered dash, it can tend to lift and bubble, expensive to fix. In the test drive check for rough transmission changes, check for rough idle from a cold start, any warning lights on the dash, and suspension clunking. The QL suspension does clunk over big bumps, especially in OR1 or OR2 modes, thats normal, but the steel suspension is known for rattling and killing shocks, look for seeping from the shocks.
4. iPhone does handsfree calls and phone book integration, the bluetooth for music is a bit clunky. Mine did read texts out, until there was an update and it doesn't anymore.
5. Map updates have been a long running saga, just recently there have been some map updates released, dealers are charging around $200 for the update.
6. Wheel well liners can tell a story, lots of holes in them may suggest rubbing tyres and offroad work.
7. WK2s all have DPFs, no adblue.
8. See point 1
9. The CD player was pot luck, some got them, some didn't. There are kits to remove them and replace with a larger console tub. It may be discussed in a previous thread on here or on jeep garage forum.
If you want to go offroad, the rear elsd is good, and that also comes with the air suspension. I have this optioned on a limited, but it can be hard to find 2nd hand. Overlands came with it standard.
Also look at chief products for underbody protection, uneek do some stuff too. The front plastic/felt belly pan under the sump is the first thing to get ripped off when offroading. Mine is 5 years old, diesel limited, done lots of offroading, been very good, no problems so far.
Oh, and a lot of info on this facebook page:
https://www.facebook.com/groups/jeep...clubaustralia/