Have you a meter to test the PRAM battery's voltage? If you have no new one (3.67V), and if the present one is under 3V, it is better to remove it entirely and go on without one. The SE/30's PRAM will not keep its settings, but that should not affect startup from a floppy disk.
What is 'weak' about the PSU? Your filter/capacitors could be defective if it takes time to reach operating voltages. You may need a new PSU, or to replace the capacitors. Don't poke about in the PSU if you don't know your way around in there. You have far more chance of a serious 'bite' in the PSU than from charge on the CRT.
Your 8-bit SIMMs must be installed in sets of four to get 32-bit width, even if the SE/30 is working in 24-bit mode because of System 6. If you cannot fudge a reliable connection for the B/4 SIMM, you must leave bank B completely empty. Just make sure that SIMMs in bank A have clean contacts and are well-seated. That Mac, as do other 1-bit B&W AIOs, uses Vampire Video, ie, part of system RAM is used for video. Poor contacts may cause display defects, which will show as normal video broken by changing anomalies. You may also have defective video contacts at the rear of the CRT, needing cleaning at least or resoldering at worst.
System 6.0.8L is a cut-down version for special purposes. You are better off with a Plain-Jane 6.0.7, or 6.0.8 from the link that I gave you, for the SE/30.
de