The "light bulbs" are neon lamps used for surge suppression. They are supposed to light up if/when redirecting excess current. I'm not sure if anyone's figured out their specs for replacement, but they're unlikely to be the cause of your symptoms.
The optoisolator is a small, 6-pin DIP package on the analogue board, the small IC-looking component labelled "U3", and located at the bottom left of the analogue board (if facing the top), next to the brightness knob. It is a not-uncommon failure point in the Mac Plus and earlier. (
Here is the wikipedia page on optoisolators if you're curious what it does.)
Whether it is the definitive source of your problems is hard to know, as many things can lead to your symptoms. The clicking you describe is likely the "flupping" sound (as described by Larry Pina in
Macintosh Repair and Upgrade Secrets) of the power supply repeatedly attempting to start and then resetting when it hits a failure condition.
U3 should be cheap to replace, so it's worth a shot and may resolve your issues. If it does not, I suggest taking a look at the previously mentioned book, as well its follow-up,
The Dead Mac Scrolls, which is a diagnostic manual for old Macs, with a list of symptoms and their likely remedies, without any extra fluff or explanations.
The original part number is "4N35". Philips made an equivalent version with part number "ECG 3041". If you're unable to find this on ebay or from a reseller, you can try searching for a 6-pin, 2500 Volt optoisolator.