ABS model brake Master Cylinder

Hey guys first time posting so let me know if i do anything wrong!

I've bought an 09 Jimny to learn about cars. The brakes are really spoungy, no matter how many times i bleed them - they feel good for about 5 min then they go back to having to put my foot all the way down! Having scoured the forum I'm getting a little confused on them, so I'm hoping for clarity. 

1. Does the ABS model come with a proportioning valve? I read in previous post that a failure to bleed this creates issues but I'm struggling to confirm whether the ABS model comes with this!
2. I'm assuming its the master cylinder that needs replacing (assuming I sort above out) - is there any difference in the master cylinder between ABS/non ABS models?
3. Is there anything else I could be doing wrong/anything else i should check for before buying a new master cylinder?

The ABS light is also on (its been on the whole time since i bought it). From what i can gather this is/will be a separate issue but thought i should mention it as well.

Thanks in advance - I'm just getting started learning about all this stuff so please bear with me

ABS models will not have the proportioning valve, the purpose of the proportioning valve is to limit (or proportion) how much pressure goes to the rear brakes to prevent them from locking up, the more load in the back, the more pressure you can apply. ABS handles this by sensing when the rear wheels (all of the wheels, not just the rear) are about to lock, and modulating the pressure to prevent locking.

The ABS light on means the ABS controller has detected a problem, this is usually a wheel speed sensor issue, but, until the code is read, you don't know, it could just as easily be an ABS modulator issue, in which case you're chasing your tail trying to get it bled, at the very least get the code read so you can be guided on the way forward.