if you bought it, it will normally have been pre treated, and should sink automatically. it will however release an incredible amount of tannins into the water, so boiling the wood won't go amiss. it will still release some tannins, but won't turn the water really dark that way.
if you have found the piece of wood, make sure its completely dry and is actually drift wood (drift wood need not be dry). i used a rather attractive branch in one of my smaller tanks and the results were any thing but positive. boil any piece of wood you find if you feel the need to do so. its better to be safer than sorry, but don't go overboard with it hahaha.
I just chucked them in my puffer tank when they were yellow and dry and they sunk immediately.
Adler cones also release tannins into the water, but I have not noticed a change in the pH using them.
Brown algae is usually cause in newer tanks, as the nitrate levels build up. is this the case in your situation?
There are some fish that eat it, like golden algae eaters, but don't get these fish for a community tank.
adding plants if you have a tank that is suitable, with suitable lighting should help out-compete the algae for nutrients.
get bristlenoses, and nothing else. you can get ottos once your tank has matured and has been running a while with no problems. they are usually quite sensitive to water conditions.
I am unsure what you mean by what tye of bn. usually when stores sell bn's they are ancistrus chirossus (spelling?) unless labelled other wise. these are the common bristle noses.