TGM has the ADA fertilizers on sale - just pick up what's suitable for the first 3 months (sounds as if you've the ADA Amazonia already)
Or if you've not got the aquarium soil, wait on deciding
I do water changes straight from the tap, (using a python system), just set my temp a couple degrees cooler than the tank & refill (fish can more easily accommodate a sudden drop in temperature than a sudden rise)
I add Prime (diluted into ~ 300ml) for entire tank volume (adding extra Prime when I can smell the chlorine blasting out of the tap)
I have the filter running during water changes - though flowrate is turned down & directed against the glass to prevent substrate disturbance
If you can't make the live Aquascaping events, just watch the live feed online (often done through both FB & YouTube)
- YouTube version generally remains available after the event but Live means you can ask questions as it goes along
I've watched most of Aquarium Gardens Filipe Oliveira event now - definitely worth the while as he talks about what he does, demonstrates techniques (volume is on the low side so need a quiet room ... or better speakers than my iPad
)