im pretty sure caps 7 and 8 are to help with noise floor, but if you use the right cap (nichicon muse es for example) it improves the sound, especially bass handling. id put them in there its maybe 2$ more in parts.
as for the resistors, 1/2 watt will work absolutely fine. they are considered overkill, but there only detriment besides cost is that they are physically larger. 1/4 watt is still on the safe side, there cheaper (not by alot, but still) and their smaller. size isnt a big concern as you are not using a production board, but if you were, you would need the 1/4 watt resistors becasue 1/2 wouldnt fit on the board.