Low water is when you want to be there- the river is steeper, and a ton of fun! It sounds like everyone puts in below #10 during the wet season, so you would miss the top half of the daily stretch.
October is pretty prime- it's hot, so being on the water is a welcome relief.
The river isn't super difficult, but some swims would be terrible- lots of big boily water in more than a few places. You'll see a lot more crocs if you go all the way down to Kariba, and there are a couple of portages.
The Zambia side is cheaper, and the situation there is currently a bit more stable, but I found the Zimbabwe side to be more convenient. Just my 2 cents.
SAFPAR and Shearwater are the biggest and best games in town in Zambia, and Wild Horizons in Zimbabwe. It's also super easy to cross the border. It's also cheaper and easier to fly into Victoria Falls versus Livingstone.
Bring a boat, and any other retired gear you have. Guides and porters will thank you for anything you leave with them.