Gotcha.
Looking at outboard boxes like the LaCie is probably the best way to go, in the vintage Mac context. 68k, and even most PPC CPUs, aren't really powerful/fast enough for anything other than RAID 0, 1, or 10 in software. That's part of why most low end RAID solutions have those three options. (That's also why lots of PC IDE/SATA cards like the one trag mentioned are "RAID!" but only really 0/1/10)
W/re 10, 0+1 and 1+0: it's entirely semantics. (well, semantically speaking: it's about configurations and which disks are at which layer.) those two and 10 aren't officially "standard" RAID levels per wikipedia but I haven't met a RAID controller from the last 20 years that doesn't support them.
A 0+1 is a mirror of two stripes. A 1+0 is a stripe of two mirrors. With those two configurations, they're typically independently configured, whereas 10 is managed as a single unit by the controller/software.
In terms of overall capacity, and in terms of better statistical likelihood of safety. E.g. with RAID 6 you can have any two disks fail, and with a RAID 10 or 0+1 you can have a specific two disks die and lose the whole array. RAID 10 does typically get you some better speed and IOPS than RAID 5 and 6 and you can do it with cheaper hardware, because the compute on RAID 10 is trivial.
RAID 5 is a popular compromise especially for 4-bay systems because you get 1-disk worth of failure tolerance and a higher capacity than a RAID 10, but lower overall performance.
Which RAID level you use really depends on what goal you want to achieve.
Anyway, one other thing to look at is RAID boxes (like that LaCie may be) that have their own controllers. A point of comparison is the HP MSA 20, which is basically a 2u disk box with a U320 SCSI port on the back. On the inside of that port is a RAID controller going to twelve SATA ports, which can have 160-gig to 1TB disks attached. The device can present as a single SCSI ID with several LUNs each up to 2TB. (At least as of the newest QuickSpecs I was able to look at, it's possible it supports more but GPT wasn't in common use then so they just wrote 2TB for convenience.)
You'd manage it with serial console or a web site. I don't know why HP thought to build this, but if I'm remembering right it was sort of at the transitional era from USCSI to SATA/SAS so it was probably both as a high-capacity upgrade for existing systems and as a transitional tool. (web/BIOS/console management is extremely common with RAID cards, on the PC/x86 side of things you can configure a card without worrying about the OS that's running on top of it, most PC OSes can boot right from RAIDs on such cards, because the OS just sees it as a single big hard disk.
The other neat trick most raid cards can do is if you replace the HDDs involved one by one they can typically grow the volume afterwards, although not all OSes handle this well.
W/re the OWC raid I've got -- it should work in os9, it's just usb/firewire storage. The only downside is 4*3TB disks will format to bigger than OS 9 can really use.
If you've got a bunch of 146-gig SCA disks, the easiest way to use them might be to find a server or workstation that fits them. I have a ProLiant DL380 Gen4 with 6*3.5-inch bays on the front, and seven 10k 146 gig disks, and a second one with two 36-gig 15k disk, although those machines are kind of loud for a home environment so I don't actually run them.
The other option is ofc to run them one at a time in your other machines.