The Wallstreet supports up to OS 10.2.8 officially. However, you need a bare minimum of a 4GB hard drive to install and use OS 10.2. Even a barebones install can take up over 2GB.
It should do OK with OS9 without adding RAM or upgrading teh hard drive.
Note: you will probably find the the WS now has a dead internal backup battery (also called a "PRAM" battery). I've replaced them in three Wallstreets but it is not a trivial matter, requiring a fairly deep teardown. Unfortunately, the source I used for new replacement PRAM batteries no longer has them. Newer G3s like the Lombards and Pismos can work without a PRAM battery but, in the three Wallstreets I maintained, we fought a herd of odd symptoms until we replaced the PRAM batteries. One computer would not boot from any Apple OSX installer CD but would boot from third-party utility CDs. Another would not charge the battery until the PRAM batt was replaced. As it's been about six years, I can't recall what nonsense the third one invented but, believe me, none were in any support documents, Apple's or otherwise!
On the three I maintained, I installed 40 to 60GB hard drives, maxed the RAM to 512MB, and installed OS 10.3 using a helper application. We ended up buying at least tow new main batteries, and two taht were less than 300mHz, got 300 mHz upgrade cards. My friend oved hs Wallstreets and did not mind throwing money at them.