Thanks JClasstraveller et al for the input. Highly appreciated indeed.

"There's not a great deal between the Hunter and Tamworth though the drive is nice". This is interesting... Living bang in the center of Europe you cannot go 5-10 min without bumping into "something", and we're looking to encounter the "nothing" - to a certain degree - as it's so diffrent to what we're used to.
We got the same (on a diffrent scale and scenery when doing Uluru last time we visited Australia). We're currently living in a landlocked country (Switzerland) so need the Ocean on the trip as well...

​​​​​​​So, we have moved one step forward in the planning - Thanks a mill.

Sydney - Hunter Valley - Tamworth, to then head to the coast via Dorrigo and pass Brisbane to The Sunshine coast rather than Gold Coast. We are returning the car to BNE before heading for 3 nights in Brisbane (w/o car)...

​​​​​​​QQ on beaches: We do not want anything crowded but nothing too isolated either. Any recommendations north of Brisbane (close to Sunshine Coast) to stay 2 nigths with one full day at the beach?
QQ on something else: Is Australia Zoo worth visiting? My better half was a big fan of the Irwin family and seems like their zoo is close by Brisbane...

Again, I cannot thank you all enough for ALL the tips and pointers. CPMaverick sharing the photo's has been super helpful as well - to set our general expectations...