We were really lucky with the weather, it was never less than 25C. I was fine with walking trainers (Reeboks). It was too warm for boots but they'd give better ankle support if needed. Likewise take poles if you find them helpful, but I personally find it easier to negotiate rocky scrambles on all fours (where poles would get in the way)
Walking sandals (Tevas and co) would be OK for the first day walk (all on roads), but no more than that.
Main thing is to be prepared for some extended stiff scrambles (up rocky / bouldery paths) - the first part of the Tiscali walk and then the climb up to Tiscali are the worst - but generally the walking is pretty much on the flat.
I thought the first 2 days were more "A" grade because they were on paths / roads without much scrambling (unless you went up Gorrupu Gorge). The last 2 walks were more "B" grade because of the more difficult terrain, but much more interesting because they were point to point rather than out and back along the same track.
I was worried I'd struggle with an A/B grade walk because I'd done almost no walking the previous 2 months due to the dire weather back home and was fine.