1. Do not go any higher than the 47 uF to the rectifier.
2. You can go to at least 200 uF to the two output transformers (after the choke)
Both of these should be at least 500 volt rated on an ST-70
Personally, I did things like this years ago on an ST-70 and found that after about the 100 uF you have on the output transformers now, adding more won't really help much.
Understand that on an ORIGINAL Dynaco ST-70 just the quad cap ran the whole B+ system for the amp - driver board + output transformers. Dynaco used a 30, 20, 20, 20 cap with 30 uF for the rectifier and a VERY SMALL 20 uF to run the TWO output transformers. The other two 20 uF sections powered the driver board. The whole amp ran on 90 uF total.
On the VTA ST70 you have 40 uF to the rectifier, the 80 and 20 are wired together for 100 uF to the two output transformers and 324 uF (294 uF on the board + the 30 section of the quad cap) to run the driver board. Set up like this, the VTA ST-70 has plenty of B+ storage to run the amp. IMHO adding any more capacitance to the VTA ST-70 as set up like this will not help the amp. The VTA ST-70 amp kit (if used with the stock parts) has 494 uF of B+ storage vs. the 90 uF of the original amp. That is 5 times what the original amp had and IMHO is enough to bring out the best in this amp.
Your question was about "capacitor banks" .. You CAN replace the quad cap with separate capacitor banks but then you run into the problem of where to place them and how to safely attach them to the chassis. I've seen the inside wiring of amps that people have added separate capacitors and sometimes they are well done but many times capacitors are glued in there with wires running all over the place. Sometimes I get flak on customer inquiries for not using a "cap board" in place of the quad cap - BUT - a quad cap is a good way to get a lot of capacitance at a reasonable price and the quad cap makes the amp look "original". A cap board like the Triode Electronics board designed by Sheldon Stokes gives more capacitance than the quad cap on the VTA ST-70 amp - BUT - the Triode cap board is rated at 500 volts and the VTA amp's quad cap is rated at 550 volts. You have more voltage "headroom" using the VTA ST-70's 550 volt quad cap.