Regarding his physicals, i highly doubt he was actively improving in that regard while sealed... he was practically wearing that baggy jacket all along so we never got to see how buff he actually was.
Also in an interview - Akutami said that outside of Toji & Maki (Heavenly restricted cases) - Kenjaku & Gojo are the cream of the crop in terms of physical ability... in a question about hand to hand combat w/o Cursed Energy & Weapons.
https://tempenensis.tumblr.com%2Fpost%2F699269909260156928
The main point.. is that Gojo was already a beast in terms of hand to hand combat. He was capable of overwhelming multiple Disaster curses at the same time using CE reinforcement alone. That's actually insane if you think about it.
Regarding his Cursed Technique, i again disagree.
He practically sharpened it to the extreme, a year after the Toji Incident. All that was left at that point were these long distance Teleportations and his Domain.
We just gotta wait and see, what this "special training" was about. But i agree with you, Sukuna did eat the remaining fingers and his body so Gojo doing some specific prep work may also be the case. It shows that the 2 Strongest aren't taking this fight lightly and i like that - as you mentioned before bro.