20uF at each node is fine.
Don't go above 40 for the first/reservoir cap with a 5Y3G rectifier. (In fact its preferable to keep the reservoir at 20uF for longevity of the 5Y3G, but 40uF will keep the bottom end tighter and most 5Y3G should handle it - although it exceeds the reservoir capacitance rating).
However, the best way of getting rid of hum from ripple current (if that is your concern) in a SE amp, is to use a whole-of-supply CLC filter between the rectifier and the OT/output tube-plate supply node. In the case of this type of amp, you'd use another 20uF cap and a HT choke, which in this type of amp (with a 6V6 output tube) can be a 3-10H, 40mA-rated choke - one of these
http://store.triodestore.com/22707.html would work fine. (If you're planning to use a 6L6 output tube, then you'd want a minimum 100mA rated choke)