don't bother messing with your pH too much as it will cause more trouble than good.
Chain loaches are good and cool to watch, don't get big and are reasonably peaceful
Clowns are awesome, colourful active and act like idiots most of the time, but don't forget that you need at least 3 (more like 5 or more) and that they grow to around 30cm +
Zebra loaches are a good middle ground, as well as golden Zebra loaches, Pakistani(yo-yo) loaches
etc... good range around there, and lotsa info on the web. do your research and don't be surprised if you cannot get the ones you like as the range in NZ is very small.
one type I will warn you about is the skunk loach, Extremely cute, active grows small so should be suitable but have a major taste for the fins of just about every fish you have. still almost worth a tank on their own.
as for puffers, check out dwarfpuffers.com, or search youtube for some cute videos.