Coal Coke takes too long in order to be produced, and it's going to be consumed too fast, especially in the heat up phase, in order for (i believe), any kind of coal coke production to keep it fed. In the server i'm playing in, i toyed around with some Computercraft, and discovered the Ultimate Tree Chopper program. I found out it does two things very well. First, it produces a crapton of saplings. It's stacks and stacks. I don't even have an estimate, it's really crazy. So biomass production is a go. Second, Firs are massive trees, so we're seeing a LOT of wood. So much we actually had to set up a voiding system to avoid overflow, because not even extradimensional barrels can keep up. Keep in mind this is just one farm. Uses 1 bonemeal per Fir, which gives a crapton of wood and saplings... Very efficient.
The Wood can be used to produce Charcoal. That Charcoal can go into solid fueled fireboxes. Not the most terribly efficient fuel, but if you feed the wood to an induction furnace, or to an Electric Furnace with a lot of upgrades, you can basically feed any kind of Boiler just off of Charcoal. Charcoal is also nice because it allows you to bypass the Coal Coke production stage of Railcraft, because Charcoal can be used to cook steel, albeit it takes 4 Charcoal to smelt 1 Steel Ingot, so it's horribly inefficient, but hey, if you have a way of generating infinite charcoal, what's the problem?
Bonemeal can be gathered in the form of a Skeleton Soul Shard, or you can set up a Sulfur Goo farm. It's ridiculously easy to set up, and it passively gives you infinite Bonemeal, no redstone required, no turtles killing skeletons or messing around with dangerous lava, just a water stream to carry the goo to a collection point and feed it to the turtle Logger. Now, the turtle can use Sulfur Goo as bonemeal, but Steve's Carts can't, so that's an advantage on using the turtle to do the logging instead of a Steve's Cart farms, or a Forestry Farm. Forestry Farms are much more resource intensive, and not quite as efficient, but you do want to set them up for Rubber & Fruit, if you like it.
So, this is how i'm fueling my Boilers. I got 1 36 HP Boiler set running off of Biofuel, and going to set up another to be fed out of Fuel until we run out of Fuel, at which point i'll just switch over to Biomass and possibly build another farm to compensate. Nearly 300 MJ/t should be enough for our needs, until we set up insane amounts of igneous extruders feeding into a recycler, feeding into Crafty Turtles opening up Scrap Boxes and giving us nearly every resource in the game. No need for mining anymore - Everything is renewable now