ESP32 and PSRAM

[sb_espressif]

Hi there; I am relatively new at hardware design, and am trying to work through designing my first esp32-s3 board from scratch, with the aid of this (very helpful!) document:
https://docs.espressif.com/projects/esp ... index.html

I am also referencing two other esp32s3 development board schematics:

• the tinys3, from Unexpected Maker
• the XIAO s3 from Seeed studio

I'm wondering if I can ask some questions about PSRAM/Flash ICs:

• The tinys3 uses an off-package PSRAM chip; the Seeed uses an off-package Flash chip. Is there a reason to prefer one over the other?
• How interchangeable are these parts typically (which is to say: how standardized are PSRAM ICs, for example? Is it the case that the pins/communication protocols for these are generally standardized and therefore swappable? Or does one need to get into the weeds with writing custom SPI code to adjust timing, mode, etc. depending on the IC?)
• When I search for the IC I see used in the tinys3 chip on LCSC, it's categorized as "SRAM". And a search for "PSRAM" on LCSC returns almost nothing. ChatGPT tells me SRAM is different from PSRAM, so I'm a little confused how to 'shop' for these parts on LCSC.
• Is PSRAM a difficult part to source currently? I ask because DigiKey (which DOES have a PSRAM category) seems to only have a small handful of quad SPI PSRAM chips, half of which are listed as either discontinued or out of stock. LSCS Has only one active listing for a 64Mbit Soic-8 chip, with few in stock. I guess I'm wondering if I'm looking for the wrong thing, or if it's expected that these are hard to come by at the moment (maybe this is why one would prefer Flash over PSRAM)?

I'm aware these questions are both quite broad and also quite immature, but as I said, this is all new to me and I'm trying my best to learn, so any advice from the voices of experience would be greatly helpful.

Thanks!