Regarding your first question/statement - You haven't seen a definitive answer on some of the settings because there isn't one. Different people have had good results with different settings, so that's what they continue to use based on "feel." Since it's such a complicated routine(in terms of how many things the model looks at, plus all the random elements thrown in for fun), there haven't been any tests I've seen proving that one particular set of settings is better than every other one.
Regarding your second question - If you assign a percentage of carrier planes to search, then that's what those planes will be doing that turn. They do not break off a search and join in your attack (although they can and do occasionally "hit" ships during the search phase itself.) As to whether you should just set all of your carrier planes to attack and rely only on dedicated search, this can work out well under ideal circumstances. Follow-up question - How often are circumstances ideal when you're playing the game? (You won't find complete forum agreement on this one either, which makes life more interesting, but personally I always have at least 10% search set, for at least one attack group per carrier.)
Lastly - Welcome to the forums! Mostly a good bunch of folks here, so if you have more questions in the future, don't hesitate to ask.