would rather reduce my plastic use and would look towards sustainable wood products
This aspect is not clear-cut: I thought
paper bags were more sustainable than plastic, but I was wrong. Here's a sample:
it takes 91% less energy to recycle a pound of plastic than it takes to recycle a pound of paper.
Transport of WRC from US forests leaves a not insignificant carbon footprint, and cutting and dragging and machining English cedar must also reduce sustainability.
Perhaps poly hives have less of an environmental impact? Perhaps leaving cedar to grow and absorb CO2 is a better option? Certainly, at the end of its life poly can be recycled entirely.
half a dozen frosts a year so thought that the need for insulation would be less needed.
Bees aim to maintain a level of warmth and humidity and any variation will require work to return the nest to that ideal. For this reason insulation is useful all year round.
Bear in mind that extremes of temperature and a poorly insulated hive will oblige bees to work: when cold, stores must be eaten to produce heat, or when hot, flight to collect water to dress the nest to improve humidity or lower temps, in addition to the work of fanning the air about; work ages bees. A thick tree trunk offers ideal insulation; how does 17mm timber compare?
I would be worried running this with no experience and am concerned re swarming
It is easier to run the Rose hive system than a hive with two sizes of box and a QX because commonality of parts simplifies the job: one size of box and no QX replicates a natural nest that allows the queen free run of all boxes
which will reduce swarming significantly.
We use the one-box system at the honey company where I work; it was the route to reducing costs and is the closest to a tree trunk format you can get, apart from a Warré. We use National deeps only unless making comb honey, when supers (or shallows) are used above a QX. Deeps are a bit heavy, but manageable; to save the back we usually use nuc boxes to cart honey to the van.
the principle of adding boxes between the brood as a way of expansion could be used still underneath a QE with honey supers above?
Yes, this is what I do: two, three or four deeps below the QX with supers above the QX as usual. The QX can be put under all but the bottom deep when the main flow is on and as the brood recedes down the stack, and deeps can either be extracted (giving good combs for the following season) or stored (to be given to other colonies or nucs).