It doesn't mean the bacteria have died off, just that the plants are taking up the ammonia. Some bacteria will still grow in the background but not as many as in a tank with no live plants.
Yes, fish should be added a few at a time (but with shoaling fish you need to add the entire shoal at once) and check ammonia and nitrite every days till you are sure they are staying at zero; then you can get more fish. If at any time you do see ammonia and/or nitrite, water changes will be needed to get them down, and stop getting new fish for a few weeks.
Yes, fish should be added a few at a time (but with shoaling fish you need to add the entire shoal at once) and check ammonia and nitrite every days till you are sure they are staying at zero; then you can get more fish. If at any time you do see ammonia and/or nitrite, water changes will be needed to get them down, and stop getting new fish for a few weeks.