This machine is 26 years' old. The caps on the motherboard, the analog-board or the PSU are likely to go soon. I would strongly recommend that you get at least the first two and preferably all 3 re-capped. There are people on sites like 68kmla.org that'll do it for you or at least sell you the capacitors themselves to allow you to do it themselves. The internal SCSI on mine went 2 years' ago and I had my motherboard recapped.
Also, invest in a new PRAM battery. They are 3.6V ½AAs. They cost about €10. The red and white Maxell brand batteries have a notorious reputation. They are known to explode and destroy keyboards. I don't think that anyone expected that machines would still be in use well into what was then the new century.
Lastly, I would recommend that you invest in a SCSI2SD. It is an adaptor that allows you to plug a micro-SD card into the 50-pin SCSI inside the SE/30. This has three benefits — it makes your SE/30 much, much quieter, it improves the airflow inside the Mac and it reduces the amount of heat generated, this putting less heat stress on the internal components. If you are lucky with your choice of HD, you can put in a 80-pin U320 SCSI drive with an 80-pin to 50-pin adapter. If you get one, be sure that it has jumpers for termination. Many U320 drives, but not all, support 8-bit SCSI. These are quieter and faster than HDs from 1990.