guppy attacking neon tetras

Question
Hi,
I owned an aquarium when i was younger and had no problems what so ever, however i have just returned to the hobby and seem to have a problem with my guppy, there are 4 guppies in all and all male, in a 60 liter tank with 7 neon tetras, 1 zebra danio and 2 longfinned leopard danios. I have numerous plants around the back and sides which are a nice combination of fake and real, the real ones are ferns and egeria densa, and numerous hiding places in bogwood and lavastone.
My tank settings are    
PH = 7.5
KH = 7
GH = around 5
temperature = 24c
No2 = 0
No3 = 0
the water flow is moderate.
And i have ran the tank for 4 weeks adding tapsafe and bacterlife to the water to moniter it before adding my fish 2 days ago.
However my guppy, one in particular (i have not seen the others do it) is nipping the fins of the neon tetras and occasionaly the other guppies.
The tetras also seem to occasionaly chase each other and have a quick nip too.
Is it something i am doing wrong?
could it be because they are all new and they are just putting each other in their place so to speak?
or do guppies nip at fins in general?

Like i said i had guppies and neon tetras together before buy never had this problem, and am concerned as to the health of my fish, even more concerned that my centrepiece's and absolute babies which i have got the tank specifically for are long finned. 1 is a golden lyretail killifish and the other is a peacock gudgeon.  

Answer
First off well done on taking the correct steps on setting up your aquarium!  Second it does sound like your fish are just setting up a pecking order, the tetras will continue to chase each other around, its normal however I am surprised about the guppy behavior, they are normally the ones on the receiving end of fin nipping, you mentioned that you have more then one guppy, do you have a pair or males only?  If you have males only you can add a few females (2 females for every male) and this will focus the guppies activity on the females rather then the other fish in the aquarium.  As for your Killie's I really wouldn't worry about them being bothered, they are by far faster then any of the other fish in your tank.