The Gōketsu are spending an implausible amount of chakra on SC training etc.
1) How much draining would be an implausible amount? We can guess at numbers but we don't know within the context what would be OPSEC breaking.
2) This is one the Hivemind can potentially answer: How many clones are we talking about here at a time? I thought we were at around 4 clones each for Kei and Akane?
Starting with Kei:
Has 270 CP
SC Startup: 150 + (N * 25) CP for N clones
270 - 150 = 120. 120/N = 4 clones + R (remainder chakra) greater than 5 (so that Kei doesn't immediately die). R = 20 CP, 4 per clone and original.
If Kei then has her full chakra replenished then Kei can work on chakra intensive training, e.g. jutsu or chakra boosting, while the nearly chakra exhausted clones can work on training which isn't chakra intensive, e.g. alertness, athletics, ranged weapons, deceit, etc.
Akane is very similar:
Has 300 CP, so 150/N = error, 6 clones would kill her. N = 5 means R = 25, which means still means 4 CP for clones and original.
Noburi had 1250 CP(!). So completely replenishing Kei and Akane originals would be 562 CP, leaving 688. If Kei and Akane make a full second batch of clones, for a total of 8 and 10, respectively (which I think puts them at risk of clone sickness?) then Noburi would still have have 116 CP.
So then another question:
3) How much CP would Noburi feel like he needs during the day to (a) still do his own training, (b) not be in danger, (c) not be obvious he's low on chakra, and (d) maintain OPSEC?
Those questions in (3) are very relevant because he wouldn't need to fully replenish during the day, walking around at half capacity might be completely reasonable.
If the clones are doing a mix of chakra intensive training and not then the chakra needs to keep OPSEC should be much easier to achieve.