Hi all, cross-posting after a recommendation to do so from the Vectra-C forums, hope you guys can help!

So the situation is this; I bought a 146k miles '05 Signum 2.2i Direct (so petrol) from a used dealers a few weeks ago for a very good price (650) because simply put I didn't have the budget for anything more. I researched the car beforehand, and scoured this very helpful forum for the most common problems before I went to test drive it, so when I heard the notorious clicking noise from the dash on ignition I though "a-ha! Someone's part-ex'd this car not knowing what that is, here's my chance to get a lot of car for my money because I know I can fix that". Everything else seemed fine, car drove great, all good. So I get it back home, follow the advice on here and solve the clicking noise (well, I couldnt get to the final mounting screw to take it off so just ended up disconnecting the recirc servo). Naturally, the insurance cost a third more than the value of the car, so it's an instant write-off if anything happens on the road.

Did a fair few short and one longer drive to give the car a good test/run-in, and all seemed great. Only thing I noticed was the coil dash light was very faintly (significantly more dim than when a light is actually on) was flickering faintly during driving. Like when a fluorescent light is about to die, that sort of strobe-like flickering, but barely visible because it's so faint. Being a petrol engine though, this light should not be relevant while driving, right? So I've put this down to a dodgy dash LED at the moment.

Then next I noticed the engine oil light come on. Checking the levels, it was low but not below the minimum. I topped up the oil - but the oil light still occasionally comes on. Came on on a short drive last night, after I even put a tiny bit more in yesterday afternoon, so it's not the oil level triggering the light.

It was last week when the real problem reared it's head - mid drive, simply changing lanes while doing about 30mph, and the engine cuts out, I lose power to the brakes and such, radio shuts off (but power to the dash lights and radio comes back). Stop the car, hazards on, engine turns over but won't start for a couple minutes, then starts right up. Five minutes later approaching some traffic lights and the same thing happens, this time there's a much longer wait until the engine comes back to life, and now the spanner light is on - but limp mode is not enabled yet (or at least my revs aren't limited).

Partway through my return journey from where I was going that day, spanner light comes back on, then a little while later my revs get limited to 3k, but I make it home fine like this.

This is then when I started bookmarking and studying every thread on here and other forums about the various loss of power topics that plague these cars, statistically it seems to be either fuel pump or MAF related, so I bought a generic OBDII reader (and more recently an opcom clone that doesnt want to interface with my car so I'm re-ordering a new one - does anyone on this forum supply them? There's another forum with someone who does but I'm not a member), but it reads no error codes.

So at the moment, when I start the car up cold, it starts fine, no warning lights, drives fine. After a variable amount of time, I may get either or both the engine oil and/or spanner lights, but limp home is vary rarely activated (only twice, and restarting the engine clears it). Reading the OBDII while the lights are on shows no pending codes, apart from once when I got a faulty O2 sensor (B1S1) code and the live data on it had errored, but the rest of the time the live data on that sensor has worked fine (very bizarre). I have not had any engine misfires that I've heard.

My challenge is, I'm already loving this car so I want to remedy the situation rather than throw in the towel (and I'm completely new to mechanical repairs by the way, willing but a total newbie), however because of the price I paid and my lack of funds, I don't really have the budget to replace any more than one part, and I'm terrified by all the repeated parts replacements other people have gone through without managing to solve similar problems. So I really need to identify with as much confidence as possible *one good guess *to then switch out and hope it solves it, and that's where I need your help, with the problems I've described.

TL;DR:

coil light on a petrol car very faintly flickers (suspected red herring)
engine oil light comes on quite regularly (45-50% of drives)
spanner light comes on without limp mode (30-45% of drives)
spanner light comes on and limp mode limits revs to 3k (10% of drives)
spanner light comes on and revs limited to 2k, speed to 20mph (just once, when intentionally driving around my block for an afternoon trying to recreate the problem)
engine suddenly cuts out (no choking) and loss of power, wait 2-10 and can restart no issues (happened on just one trip but twice within 5 minutes of each other)
I've put a pressure gauge on the test valve on the fuel pump and it went up to _54k when I charged the line (engine not started), and then did slowly fall to _32k over 5 minutes where it seemed to hold. After starting engine and watching it respond normally to revs, I released pressure and tried charged line again and it held pressure much better this time, but still fell to _46k over 5 minutes.
Generally no pending or stored error codes, though one O2 fault as a one-off, been fine since.

The car has done enough miles (with at least one previous owner not looking after it) that if I took it to the garage I feel fairly confident they'd recommend changing basically every part and sensor in the engine bay, which obviously I can't do, so - please help! haha.

I have a long drive approaching next week to transport some family members from london to devon for a family occasion so I'm very worried about that trip at the moment!

Thanks everyone!