So, let's say that we have a redstone block in the middle of nowhere and I want to power as many command blocks as possible using that one redstone block. No repeaters are allowed, and there are infinite space and redstone(but still, no repeaters). What is the maximum number of command blocks possibly powered by this singular redstone block? And, if you can find it, what is the layout of this efficient design?
With chain command blocks, infinitely many, since you can just set them up back-to-back, and powering the first one triggers the whole chain (assuming the rest are set to not need redstone).
Without chain command blocks, still infinitely many, because you can invert a redstone signal twice to refresh its power. This is more or less that a repeater does, if you think about it - it's crafted from two RS torches. Without a repeater, you can cheat and just put down two NOT gates :P
Without those, you still have a lot of options for extending a redstone signal like probably using hoppers and comparators or something silly like that; I'm not too sure, but the above definitely works.
For what you want to do, chain command blocks are... probably what you want?
If chain command blocks is not allowed either then the answer is still infinite. We can still move the redstone block to power the next command block. Besides, we can still use "execute if" to simulate chain command blocks.
If that is not allowed then we can still use the first command block to create more command blocks with the "require redstone" flag turned off. Naturally, these new command block would be configured to spawn more command blocks ad infinitum.
If using fill commands to move the redstone block is not satisfactory then we can still create a piston with a command block that will move the redstone block to the next command block and repeat ad infinitum.
The answer is simply infinity.