I built a series of square 4'x4' wood 'rings' with bottom corner pegs so a ring locks into the previous one against wind and large vermin damage. I can add or subtract rings as needed and it is working very well. There are no true air spaces in my system but there are enough small gaps between the rings to allow air. Plus, I turn this heap more often than I did with pallet type bins and I'm getting compost faster. If air worries you, simply buy a 3 foot or so length of 6" poly waste pipe, drill a lot of holes all around, attach an end cap at the base and stick into the centre of the heap or build the heap around this pipe.
I never found leaving air gaps in the wood sensible as we all cover the top of the heap to retain the heat. The more often you flip, the faster the piles heat up.
I could afford only cheap spruce wood which would rot quickly so I primed and oil painted mine with 2 top coats and they should last much longer. Mine are also very visible from the road so I wanted them to look neat. The base rings were all pressure treated wood as they'd take the brunt of all moisture. You can treat your main wood but do consider whether or not your product could leach out of the wood and into the compost, specifically carcinogenic elements in the product. Each set of my bins sits on a piece of 1/2" weldmesh which keeps out vermin and allows in worms. With your 1" thick planks you'll need to add more vertical supports for stability. And some sort of lid is always a good idea.
Size wise, you can build it 8x8, provided you can get into it for turning the contents. I personally find a series of (2"x6") 4'x4's (approx) sturdy and easier to work from and good use of my lumber. By the time the season's first bin is full enough, I can leave it and start a 2nd. The first bin has time enough to break down and be flipped into the next where I can stack the now unneeded rings of the first. The 2nd bin is a bit slower due to the later season, but will eventually be flipped. The 3rd bin is our winter bin as its too late for much composting breakdown so it holds all our household winter offerings. Heightwise, if the bins are fixed, its better to have a front access panel of some sort. With mine, I simply take off a ring at a time which I find much sturdier than previous bins which bowed at the sides after time and front doors wouldn't stay in.
I'm finally getting around to building flip up lids for my bins, again a 'ring', one that's angled and will have sheets of metal shed siding which I got free from our local tip. Couldn't believe my luck that they were the exact size I needed. Lids will keep out excessive rain as well as climbing vermin.