You need a new 2.2uF 275v capacitor in the fan, it has gone low in value, and as well the grease in the bushings has gone hard, and needs to be relubed with regular engine oil. Some have a split capacitor with 3 leads, one section is 0.5uF, the other is 1.5uF. Easy to tell as it has 3 leadout wires.
As to blade number, it makes no difference, the motors inside are likely the same cheap motors made by assorted small vendors using the same patterns, they are all cheap and nasty.