First, welcome to the site. While my expertise is on the older Isuzus, there are some common factors, so I will give it a shot.

When you say that it just clicks, that sounds like either a starter issue, a battery issue, or a wiring issue. If your battery is the original, it is way past its expected life expectancy.

I would start by checking all the wiring to the starter, both the primary and the secondary. If there is any sign of corrosion (green corrosion) on the primary cable, the big one, then I would replace the cable. If there is corrosion showing, then there is most likely corrosion under the insulation that you can't see.

If the wiring checks out, then I would suspect the starter.

The one symptom that isn't consistent with this analysis is that occasionally the engine dies after a few seconds. That is consistent with a faulty fuel pump relay. The relay is by-passed during the start cycle so the engine will start and then shut down if the relay is bad.

Since once the engine starts the starter circuit is no longer active, you have presented two different sets of symptoms that aren't necessarily contradictory, but may indicate more than one issue.