Yeah, a KH of 4 is indeed soft. You can add baking soda to help buffer your KH and keep your pH from crashing. You have good water for SA cichlids and soft water fish. This also means that you will need to find out exactly how long you can go between water changes before your pH starts to nosedive, giving you your water change schedule once you have fish in the tank. Note: this will be different than your fishless cycle though unless you plan on heavily stocking your tank right away. You will get a feel for it.
In the meantime, you can add baking soda to buffer your KH. This will help you finish your cycle in a timely manner. Add 1 teaspoon every 10 minutes until you get slight rise in pH.
It's fantastic when you start getting reults like that... .. well done !
The fact that you are getting Double '0's within 12 hours says your cycle is pretty much over... but obviously, the longer you can continue to prove it, the better.
I didn't fully stock after my cycle...i added a dozen or so inch long fish and continued to 'up' my bio-load in weekly stages.The theory behind our fishless cycle is, though, one that allows us to fully stock straight after our cycle, so it is possible should you choose to.
There is the chance that the bogwood MAY lower your tanks' PH once you introduce it, which brings me onto my next point, a PH 'buffer'. I have soft water like yourself from my tap so i have to add a good handful of Coral Gravel to keep my buffering capacity high and stable, therefore a higher and more stable PH. It's something you may want to consider as a PH crash after your cycle can be a nightmare (!).
Best of luck with it, always encouraging to see a great (first?) fishless cycle.