They will be more active at night since by nature they are nocturnal. Lessening the overhead light also works to calm them; have the tank as dimly lit as necessary for the plants; a layer of floating plants is ideal to achieve this, and they will be out more just with that. All nocturnal or semi-nocturnal fish will be out more in dim lighting.
Providing lots (and I mean, lots) of hiding places is necessary or they will be highly stressed. Groups of 5-6 or more will lessen their timidity and stress, but they still need refuge. Interestingly, as with most similar-habit fish, they are out more during the day if they have plenty of hiding spots to disappear into, it seems to calm them if they know they can escape. Their need for this is why they are so often trapped and caught in filters, even undergravel plates. They can enter the smallest openings, looking for hiding spots.
They also like leaf litter on the substrate; in their habitat they spend hours turning over leaves and searching under them for food.
They should always be added to an established tank; however, with plenty of plants there will be no cycling issues, which gets back to your original question. However, established means more than just cycled, and it takes a couple months for most tanks to settled into a biologically established state. Avoiding any fluctuations in hardness, pH and temp will help, as will weekly water changes with water close to the tank water in parameters.