If you are getting males and females they breed every 4 weeks. Get more females than males at a minimum ratio of 2:1. Flakes are fine but they will eat brine shrimp, bloodworms, microworms and algae pellets which are fed if you have catfish in the bottom of the tank. If breeding or wanting them to multiply supply some floating weed in the top of the tank as the mothers and other guppies will eat the fry as they pop out if given a chance.
Keep the water clean, regular water changes are always good. I am assuming you have some sort of sponge filter or underground filter attached to the air pump.
Imported fancy guppies are very nice but can carry disease which they are resistant to. Quarantining before placing them in tanks with NZ bred guppies may help but I am not certain. You may need to keep them separate.
Can I suggest that you post any further queries on guppies in the livebearers section as you will get a response from more experienced guppy owners than I.
microworms, bbs, some crumbly mix (can't remember what its called and its too hot today to walk out to the shed to look), bloodworms (not often though), and once in a blue moon, flakes.
They also quite like the algae discs I throw to the bn.
I would do it like this
week 1 - change 1 bucket of water every day for a week and vacuum 2x.
week 2 - change 1 bucket of water every 2nd day for a week and vacuum 2x
week 3 - change 1 bucket of water every 2nd day for another week and only vacuum at the end of that week. If there is a lot of muck on the bottom of the tank (I can't remember if you have bn catfish in this tank or not) then the filter is not working as well as it should be (all bn and plecos are messy).
Check your ammonia levels every 2nd day. If every thing is okay you should then be able to go to changing 50% of your water 2x a week and vacuuming once. If everything still tests okay after a further 2-3 weeks one 50% change once a week and a vacuum will work.
Just remember when you vacuum not to remove every last little crumb of waste.
Then if you wish to add more fish its up to you but keep them in a seperate tank for about 4 weeks to make sure they are not carrying any nasties.
not sure what 'stone vacuum' is - do you mean still vacuum once a day.
The answer is no, if you vacuum too much no bacteria will build up and it will be as if you never have let your tank cycle. I vacuum thoroughly once a week in my big tank and partially in the open areas at other water changes.
I saw some threadfin rainbows in the lfs and they were just very plain uninteresting fish to look at. There must be others around that are better looking I think.
Sometimes fighters and guppies are okay together - each fish has a different personality and in a planted tank with some swimming areas they are often okay. It depends if you want to see what happens.
With regards to the ammonia the more water changes you do the better until you get it sorted.
Would it be a problem to do a bucket a day?
West coast beaches like Muriwai are great if you can swim. If you are taking a boogie board take flippers as well. Long Bay is good and safe. Be aware though that if the day is hot there will be queues, leave early to get a park and make sure you take plenty of shade and sunblock with you. (lessons I have well learnt).
My bn occasionally do it but not on a regular basis however they do not hit their heads as there is a big enough gap between the water level and the lid. I assume they just come up for a good amount of air.
My current batches of fighters are too young and small to swap for anything yet but they are also not suitable to go in with guppies as the guppies will nibble at the male fighters fins and tail and the fighter may eventually retaliate and nibble back. However further down the track - in another couple of months or so we may be able to do something depending on what you have in your tanks at the time.