Painting wood on walls?

ok 3 bedrooms upstairs have real wood on the walls.it used to be an Attic converted into 3 bedrooms,now this wood on all the wall has been there since we moved into the house as a child in the 70s.so now i want to paint over it,ok now i know i have to sand the walls and prime them and also use wood filler in any holes or indentations.what kinda paint works well on wood walls?flat?satin?ETC...also what the best way to paint them roller brush,paintbrush.or the technique used by some painters that use a Spray gun i guess it is.one painter wants to use a spray gun,,is that a good idea for wood?also how to prevent the wood from bleeding Thur and paint peeling