Welcome: Deej, you will like things here; a great bunch of folks looking to help. A word of warning on the CZ, in all likelihood you will feel the need for a Varmint before long. Nothing wrong with the American, The heavier barrel just makes things that much better.
That being said I Have a 204 in a Varmint, as well as the American. Each rifle tends to shoot very well, although my American took a little more to eek the best accuracy out of her. Neither rifle seems sensitive to OAL. I am sure the insensitivity is due to the long throat.
I have seated anywhere between 2.245 out to, 2.32 and generally prefer the shorter OAL for consistent smooth chambering. H4895 is a good powder to start with. Two additional propellants that I will recommend one give a try are RL-10X and my favorite, Varget.
If you work up to a max load of Varget and don’t find an accurate combination to keep those 39gr SBK’s inside of a nickel at a buck ill be surprised.
Good luck
