To make a long story short:

•Dell Dimension XPS T700r (P3 700mhz, 256mb ram) I built from advice in that linked topic (didn't get 1ghz upgrade to work, so it's stock 700mhz)
•Startech SATA to IDE adapter with Crucial 120gb SSD, formatted to FAT32 with 4K Partition Alignment per this tutorial
• GeForce ti4600 AGP video card, Audigy 2 ZS Gold and ESS ES1869F sound cards

I put in Win 98 SE CD. I get prompted and choose: boot from CD, then Start Win 98 setup, then blue "to setup windows now press enter" screen, then "setup is now going to perform a routine check on your system" remove any floppies and press a key to reboot - it's supposed to go to this Microsoft ScanDisk screen:

But I never, ever, get to that ScanDisk screen. Just stuck in a boot loop over and over again. I've tried four different Win 98SE CD's: 2x from Winworld, 1x that worked on my other P3 - all burned 4x on Verbatim Data life plus CD's - AND tried a real but scratched retail disc I bought around 1999 🤣.

I then boot with CD-rom support, and in DOS manually run the windows Setup.exe from the CD. "Setup is now going to perform a routine check on your system" (i.e. ScanDisk) - quick blue flash then it quits back to DOS. Then run "setup /is" which is the "Do not run ScanDisk" option. I can then install Windows onto the SSD, and it seems to complete successfully. If it matters, I was NOT able to make a 3.5" startup disk during the installation for some reason (known working new-old-stock floppy, 1.44mb formatted, which I updated the BIOS off of so I know it works):

Anyway, when I restart after Win98 install completes, it checks RAM and everything normally, then I get a single flashing _ on the top left of a black screen - it won't automatically boot into Win98. If I put in Win98 setup CD again and boot to command prompt, I can go to C:\ drive where all the Windows files are on the SSD. When I manually boot Windows from DOS, I get this error:

VFAT device initialization failed
A device or resource required by VFAT is not present or is unavailable. VFAT cannot continue loading.
System halted.

Googling and only thing I can find is that the SSD was maybe formatted wrong? (yet Windows still sees the SSD, lets it install on the SSD, and I can move/copy/delete off the SSD?). Others say it's an error in the config.sys dealing with IFSHLP.SYS and/or setver.exe? I've tried every combo there and still no go. ...getting at the end of my witts today already... between installing those parts (and that friggin Asus Slot 1 to 370 adapter not working) I've already spent 8pm to 5am last night, and 11am to almost 4pm today and can't even get windows friggin loaded!