For a 5G tank,you can cycle with one fish in without stressing it (IMOHO)
Use the filter,but do water changes as per an non filtered/non-cycled tank and it will cycle itself (as long as you dont wash the filter media or decor/gravel in tap water).The benefical bacteria will build up in your filter media over the weeks.
Use a liquid test kit to check the progress the cycle (ammonia then nitrite then nitrate) to know all is well.
As mentioned Java fern and Anubias are good live plants that dont need much light (8-10 hours from a normal fishtank light is ok) and dont need any extra help,plus they will help with water conditions.
Make sure you have a heater though to keep the water at the right temp.