You can also use a water line instead of a hopper line to dramatically increase the rate, water on hoppers with items on the edge. This with a carpet duper can supply as many furnaces as you want, you just need more dupers.
I wanted to avoid any duping methods since they can be patched and seem cheaty personally. Part of the fun is figuring all this out with limited fuel sources.
Shouldn't the self-supplied adjustments also apply to charcoal? Also, the furnace array for kelp can actually be a smoker array, so it can be a lot smaller than the furnace array it supplies with fuel. IMHO the main benefit of bamboo and kelp is that you don't need to harvest them explosively. That makes farming them a lot more compact than any tree farm with a comparable bonemeal consumption.
When it comes to tree farms the yields are so high they tend to break all the numbers. Even a 500 log per hour design will get 2k planks, enough for 8 furnaces continually supplied, on par with the bonemealed bamboo. And it uses less bonemeal at the cost of a blast chamber.
Did you do a calculation for how many bamboo plants are required per furnace if you don't convert them to planks or sticks? I currently have a giant bamboo farm feeding into my furnace array, and have always been curious how much efficiency I'm losing by not converting them to planks.
There is no reason not to convert to sticks at the very least. It doubles the number of furnaces that can be supplies from a single hopper line. Converting to planks would let you smelt 3 items instead of 2 at the cost of 1 additional bamboo. Unless you are worried about wasting fuel, planks are definitely the way to go.