Hello, picking up from Hertz on William St and then connecting to the bridge / tunnel over to the otherside is super easy.
I also recommend the journey from Calga up to Wollombi, it is an amazing road - roughly 200 years old in parts and the convict built elements are still very visible and signposted. Indeed stop in Wollombi for a coffee, sandwich. You could then keep going up towards Muswellbrook, gorgeous Scone and the New England via the Liverpool Range. This is also incredibly scenic and then to Tamworth & Armidale. Head down to the coast (which I think is one of the best pieces of coast line) via the Waterfall Way. Go north to Maclean (worth a short stop and leg stretch to see a lovely living small town) and then to Byron (perhaps stay just south of Byron where it is less crowded). Note traffic is generally highly congested due to poor urban & growth planning. Make a side trip for lunch and gift shopping in Bangalow. From there head north along the Tweed Valley Way (great road) calling into the Tweed Valley Art Gallery - one of the best - compact but has a fantastic Margaret Olley exhibition and then on to the border driving along side the river.

