Sye
1) I don't think a piece of wood will affect the pH, but I could be wrong. Your fish would prefer a lower pH than 8 though.
2) Grow on the wood? Java fern will attach itself to the wood, and so will java moss, but those are the only two I know of.
3) Beneficial bacteria will grow on all surfaces, including wood.
4) Sorry, can't help with this.
5) None of your fish need bogwood, but the loaches would be happy to get something to hide in.
MANY_A_MOLLY
Driftwood is found on beaches, in saltwater. It's usually bleached gray. By definition bogwood comes from, as the name suggests, bogs. This in turn has a dark color.