He really will have no money to spend other than the MLE (about $9 million) for teams that are over the cap.
Millsap and Plumlee leaving will not clear any cap space to sign players when you consider
1) Denver is already $20 million over the cap. So $20m of the "salaries saved" on those two, is just clearing luxury tax room, which can't be used to sign players anyway. So that leaves $20 million to spend on free agents (40-20 = 20)
2) Then you consider that Jamal Murray is jumping from $4m to $29m, and that takes up $25 million of cap space, so that in itself now brings you back over the cap. (20-25 = -5)
3) The cap as far as I am aware will go down a bit in 2020/2021, so that in itself will take some further cap room. Say $5 million.
So I would not expect huge upgrades with cap space. That being said Denver is in tremendous shape anyway with what they will retain, and Millsap and Plumlee can be partially replaced with the MLE. But upgrades will not be possible through FA anyway.