and how do you know if something might be working with OS9? or in certain models of G4? :/
i will only go for stuff which i dont have to flash, solder and test myself. plug and play, like a mac should be. 
however, my main mistake searching components seems to be to search ebay only on the .de TLD.
seems many offers which are only on other sites would also ship to germany.
Flashing will be definitely required (by software). In particular for "9". On "X" we can get away, but still desirable on the PowerPC systems.
The way it going to happen:
- there will be a driver (for "X") and a "9" / "X" universal executable, i.e. "flasher".
On i386 and x64 the entire thing will work without flashing, just by placing the driver where it does belong to.
On "9" the flashing will be mandatory.
There won't be i386 / x64 boot ability for now because I don't want to start with learning UEFI. That will come later if necessary.
For the rest the boot ability can be ensured by (software) flashing.
BTW: the current PMP code (be it "X" or O.F.) found in 3132 / 3124 was never updated for later PMP-s, all of them have channel enumeration bug.
This is a different bug than what is in the 3124, it's just that the number of channels is being shown one less, than expected according the standard.
As a result some trivial external drives (the tri-interface of OWC for instance) do not work at all: these external one-drive enclosures have a hidden port multiplier and it shows incorrect number of channels. These enclosures did not exist at the time SImage and myself wrote the two competing "X" drivers.
The chance SImage does update their driver is pretty much zero.
I will try it to do this year. Looking at the clock it's not a very long deadline.
The flasher is aimed to flash pretty much everything I know and there won't be any lock in the "X" driver.
Our "friend" in HK will lose his great business with these two third-party SImage cards probably sooner, than he sees the fireworks of 2020.
But be careful: no 3124 does support MacOS-9 natively yet, "SIM" for 3124 to this day never existed.
The reason is that by the time the 3124 was made, not only "9" was pretty much out, but even the sign for PowerPC was all over the wall.
Thus, no one did invest time and to be honest... with proper tools the situation today is much better.
As far as these cards: the most important is the size of the ROM. I will update this thread with the absolutely minimal ROM size requirement.