Save the NOS tubes from your Calypso and use them in the IO, the IO is one of the finest phono stages ever built, I don't think you will ever regret going that way.
Callisto is equal to the IO, one of the best ever. Take this one step at a time, go for the best you can afford even if you have to wait on the other until later. In the end it will save several exchanges and trades and you will wind up with less money spent to be where you want to be.
As for standard versus upgrade, Aesthetix can upgrade later and you only pay for the parts needed to take it to the next level. Call Glenn (at Aesthetix) and ask, he's a great guy and easy to talk to.
