So, I'm going to tackle the "custom firmware" questions.
This variant of the Galaxy Grand Prime won't see a custom rom soon, or better, probably never. Why is that, you may ask?
First of all this phone has passed its life span. Remember, Samsung phones have a life span of ~2 years, so official updates by Samsung either for the ROM or just the Kernel will never come out again.
Second reason, this phone doesn't have active developers, and, because of that, doesn't have a vendor tree which you require to do any custom rom (Lineage OS, Resurrection Remix and so on).
Third reason, this phone is based on a PXA1908 SoC which there is only one more device, at least that I know of, with this SoC and that is the Galaxy XCover 3 that is also dead.
I'm sorry to say, but this variant will share the same fate as the XCover 3.
This variant of the Galaxy Grand Prime won't see a custom rom soon, or better, probably never. Why is that, you may ask?
First of all this phone has passed its life span. Remember, Samsung phones have a life span of ~2 years, so official updates by Samsung either for the ROM or just the Kernel will never come out again.
Second reason, this phone doesn't have active developers, and, because of that, doesn't have a vendor tree which you require to do any custom rom (Lineage OS, Resurrection Remix and so on).
Third reason, this phone is based on a PXA1908 SoC which there is only one more device, at least that I know of, with this SoC and that is the Galaxy XCover 3 that is also dead.
I'm sorry to say, but this variant will share the same fate as the XCover 3.