I think bunnings has coco in block form. You want coco without feed in it preferably. You may find a lot of the coco in garden stores have fertalisers mixed in which you want to avoid. But if you can find something without feed, I don't see any reason not to use it. Probally going to save you some $. Might be worth rinsing it, as some cheap coco can have salt in it. As coconuts are often grown near the sea.
6.5 should be okay. The chem ferts mixed full strength will normally take you from a ph of 7 to 5.8. so since you have a slightly low ph, just mix the more lightly at 2/3 of the recomended strength. E.g. 2ml per lt instead of 3ml per lt. I normally do this and have to use ph pown to get it right. But you should be close to spot on by just using a bit less.
There are some one part fertalisers that are powdered. General hydroponics makes one. Koolbloom or something. Makes heaps and would be convenient to post opposed to using a heavy liquid fert considering your distance to a shop. Tomato magic would also work well, or any other soluble fertaliser for tomatoes, but you may need to check your ph with them. A cheap liquid ph testing kit is fine and often more reliable than a ph pen. Landmark or elders might have something in bulk super cheap. But you need something soluble so you can mix it properly with water.
No reason organics would not work also. But you are not trying to build healthy soil with coco, just make sure the correct food is avaliable to you roots.
The main difference with watering coco is that you don't want your medium to ever dry out. There is a lot more oxygen in the media so you can water quite often and disregard wet dry cycles that are needed with heavier soil mixes. Each time you water you correct the nutrient balance in your coco, so they always gave the correct tucker.
Outdoors coco and indoors coco are the same thing. The only difference maybe is that it is good to mulch your coco outside to prevent wind drying out the top of your pots. But any technique used indoors for coco is the same as outdoirs except you are using the sun instead of a light and wind instead of a fan.
Hope that helps a little.
hope you surpass your goals!
