won'y the guppies over stock my tank by breeding
Not if you buy all females.
Joanna69 Id personally ignore the fluval stocking advice and follow the advice on here which is from a huge number of experienced member. 1 inch per US gallon or 1cm per litre if youre feeling metric.
1 inch per gallon isnt exactly experienced, sorry.
You need to concentrate on the fishes waste production and surface area, as well as filteration.
Guppies get at about 1 inch when not including tail. You could go with 5 males, 5 males is minimum in a group of only males as they will be agressive otherwise. Maybe you could give the females away unless you want to put up with fry.
Neon tetras are very low waste production fish. This is why most planted aquarists have them. They may not be hardy when you first get them because of the lfs movement stress, but once they settle in 5-6 is a good ammount since they like to school. no less than 5.
You could try any cories. I wouldnt bother with peppered, but you could try julii or bronze ones? They get to about 2.5"
In total you'll have about 17-18" of fish, which is fully stocked.
So, 5 neons, 5 small other small tetras or guppies. and a few cories