You won’t need the IDE/SATA bridge adapters if you eventually go with an mSATA config(s) as examined here:
(Costs have come down to the point they're competitive with the old SSD + adapter route.)
https://macos9lives.com/smforum/index.php?topic=5955.msg52638#msg52638AND for dual boot scenarios... format and partit
ion first with Drive Setup 2.1 and DON’T install OS 9 yet. Instead, after formatting and partitioning... install OS X Tiger on your 2nd partit
ion (after reformatting ONLY the second partition with Tiger’s Disk Utility). Doing this will allow you to disable or omit the first (OS 9 intended) partition from Spotlight’s prying eyes BEFORE even installing OS 9 on the first partition.
All the above to avoid dreaded BTree errors & corruption associated with such dual boot installations.
THEN go back and install OS 9 on the first partition which remains formatted with Drive Setup 2.1. And yeah, you can road test all of this first with your original HD.
As for the exhaust air temp question... there’s a common ignorance that as long as these now nearly 20 year old machines are running fine and not exhibiting any blatant symptoms of overheating, that there’s really no need to clean and renew their heatsink paste. AFTER 20 YEARS! Only a matter of time, ehh?
Anyway, after extensive temp tests here with various versions of the G4 Mac mini - I found that in those minis that had not had paste renewed, that their exhaust air temperatures (from a cold boot) would often reach or exceed 110˚F (after only 15 minutes of runtime). So if your exhaust air temp reaches or exceeds 110˚ after 15 minutes, well... there’s your sign. (Fan racing or not.)
*I’ve supporting images of one of those showing where its’ paste had dried and powdered in some areas, thus losing optimum heat transmission. (Currently those images are now 600 miles away.)
But this might be of some interest:
https://macos9lives.com/smforum/index.php?topic=6875.0AND...
https://www.youtube.com/watch?v=_7iXw9zZrLoCheerio