1. What are peoples experiences with Absolute Aquarium tanks and cabinets, alternatives?
I've never had a problem with them, decent quality and price point is OK
2. Pumps - what is nice and quiet, LpH I should look at, thinking 5x display volume, multiple pumps ?
Vectra's are OK, they are a DC pump so they whine a bit. A cheaper alternative to vectra but just as quiet are jebao/jecod DCT pumps, look at fishstreet for these. Otherwise, lagunas are great pumps, eheims (the old bricks not the new ones) and lastly, aquabee pumps.
3. Plumbing - Hole through back or weir + vs - , best way to plumb to minimise noise.
Either are good when you use a durso standpipe to control the noise.
4. Stock - now the new laws have stuffed it up what Tanga's are available locally?
Plenty of tangs around, with a tank that size, tropheus sp, featherfins would be good fish to keep. depends on what you want to do with the tank, display or breeding.
5. Air / Circulation - air pump recommendations and setup, wave maker vs power head
Go the wavemaker, check out the jebao wavemakers, i have the rw4, going stong for almost 2 years now, as quiet as a vortech but not as quiet as a tunze. Use 2 or 3 of them and you shouldnt have any problems keeping detritus in suspension.