OK, first, a few tips to avoid making the situation worse: first, don't crank it endlessly as you were doing there. If you don't have fuel without air in it getting to the injection pump, it is not going to start, and cranking it continuously like that is only going to burn up your starter and battery. As you know, when it has a properly primed fuel system, it will start almost instantly. If it doesn't start right away, then the fuel supply problem needs to be fixed -- cranking it like that will not make it cure itself and will cause additional expense. Second, once you do get it to start, do not "give it gas" like you were describing. Racing the engine with the transmission in park or neutral will damage the trans due to the design of the ZF automatic, and it won't gain you anything. Once it starts, it should run just fine without needing to be revved above idle speed. Third, those of us trying to help you here recommended that you install your electric pump in line
BEFORE the fuel filter. You have it installed AFTER the fuel filter, just ahead of the injection pump, which means any junk in that electric pump will be sent straight into the IP, potentially causing damage to it. If you want this car to get back to proper health, you need to not jeopardize the IP. That fuel pump MUST be placed ahead of the fuel filter!
The good news is that you have found your problem and it will be very simple to fix. The air in the line that that electric pump is pushing is the answer. There is air leaking into the fuel system either at or before the fuel filter, and there are only a couple of places where that can happen. Once you find and repair the air leak, the car will run as nicely as it did before and you will be a happy Volvo owner again.
Here is what I suggest you try next: take that electric pump out of there and repair the fuel line between the filter head and the IP, and install the electric pump instead in its proper place upstream of the fuel filter. Use some kind of transparent fuel line connected between the electric pump and the fuel filter so that you can see what the pump is pushing out. Energize the pump, crack the injector unions open, and see what happens. If the pump was pushing aerated fuel when positioned after the filter, but pumps clear air-free fuel when connected before the filter, then you know that your point of air ingress is at the fuel filter (and almost undoubtedly you will be led straight to it by fuel leaking *out* of the fuel filter under pressure at whatever point air was previously leaking in). If, however, the pump is still sucking air even when placed before the filter, then your air ingress point is elsewhere in the fuel line, again either due to a hose failure or a severe restriction in the line.
At that point, you need to start looking again at your fuel lines. On a Volvo this is easy because almost the entire line is metal, with only two rubber sections -- the part running from the metal line to the fuel filter housing in the engine bay, and the part running from the tank pickup to the beginning of the metal line underneath the rear of the car. Check the metal line for rusty spots or any sign of fluid leakage, and check both rubber hose sections for any damage or swelling or leakage. If there is no obvious issue, disconnect the line at both ends and blow through it in reverse direction with compressed air (or even your mouth). It should move air easily. Now connect the tank end of the line to an external can of diesel fuel, and run the return line in there too (disconnect it from the tank as well). Prime the fuel system as described here earlier, and the car should run correctly immediately.
If it does not run immediately, and still has air coming into the fuel line even after eliminating the fuel tank from the system and fully priming the system according to proper instructions with the use of an electric lift pump, that will mean that there is still a problem in the fuel line that you have not found yet. If it does run correctly at that point, as I suspect it will, then your issue is within the fuel tank, probably caused by a clogged fuel pickup. At that point all you need to do is disconnect the fuel filler hose and remaining tank lines, drop the tank, clean it, and reinstall. The car will be as good as new.
This is not a serious problem and finding and fixing it won't be that hard! Let us know what you find.
George