Hi Mick,
If you are happy to travel to Wyong. Shents are a Jeep specialist and are great to deal with.
https://www.shents.com.au/
Before you look at ECU tuning, buy yourself an iDrive throttle controller. They are around $245 and you'll be very surprised at what a difference they make to the Cherokee.
I could be wrong here but there has been no map updates since 2016. I'm sure someone on here will have better knowledge than I. I don't find the lack of map updates an issue, I'm happy with mine.
Petrol brand makes no difference. 91 is fine for the petrol model however, I'd recommend running at tank of 95 / 98 through it once every couple of months.
2011+ WK2
As for issues, not really, there has been a few recalls for the WK2 so just make sure these are up to date.