As far as physical placement, I don't see any reason that you would need to separate the drives... better to keep them congregated so that if/when you add more drives you don't have to move the existing ones. (though even if you needed to it should be fine since the drives are id'd by their unique id's, which means it shouldn't matter if they change which port they are on).
Separating the drives would likely have some impact on performance and longevity, but not enough to worry about in my opinion. Hard drives are pretty much a solved science at this point, and they are designed to operate in proximity with each other. Enterprise drives may be built to handle this better than consumer units, but in a small chassis use case like this even that probably won't make a significant difference.
Physical placement won't affect the pool creation directly, that would be more related to which order you plug your SATA cables into the back plane. Even then, it doesn't really matter, it just may change which drive exactly is 'sda', 'sdb', etc.
Are you planning to use a HBA card. or native SATA ports off of your motherboard? For 10+ drives I imagine you would need an HBA eventually, but if you are starting with only 4 plus a boot device you could probably do that on most motherboards.
If you are using an HBA you may be more easily able to plug the cables into the backplane in numerical order, which in theory would set things up so that your left most drive would start as 'sda', and then proceed through the alphabet, with drive no. 10 being 'sdj', and the boot device potentially being 'sdk'.
(And no, I totally didn't have to count out the letters of the alphabet to get that answer... why would you ask such a silly question?? 🤣)