rockm

You're a little unclear about what's going on. Was this tree recently collected? or has it been containerized for more than a year?

Those are important points. If it's recently collected, removing new growth, or any growth now could seriously weaken the tree and slow root development. It should be put in a deep growing container, not a bonsai pot, immediately. A large plastic bucket with drainage holes punched in the bottom will work. I have used a five gallon bucket that once held bulk maraschino cherries (any plastic bucket, like a $5 plastic paint bucket from Home Depot will work too).

Also, if newly severed roots are exposed to sun on their tops, they could die. They need to be buried at least four inches under the soil surface for a year or so to recover from collection.

As for keeping it in a tub of water, don't. Won't help much, may even slow it down. Well watered bonsai soil heavy in organics will work much better.

Regular bonsai fertilizer is fine. Miracid fertilizer isn't "acid" it's formulated to be taken up in already acidic soil. If your soil isn't already acidic, you might as well be using regular fertlizer. BC will grow in just about anything. Doesn't need overly acidic soil. Basic bonsai soil will work fine.

I doubt you have a knee. BC bonsai with knees are very rare and command higher prices. Knees don't develop very well in containers. If your tree has little root mass, knees aren't likely.

You may have confused root buttressing with knees. Knees are separate from the trunk, rising like cave stalagmites from the soil surrounding the tree. Root buttresses are big flares almost like rocket fins coming off the base of the trunk as it enters the soil.