1. do i need to use fertilizer when i set up
For simplicities sake you need to cycle your tank first. This takes at least a month generally speaking. Most of your plants will be fine during this process except for the HC. You can probably kiss that goodbye no matter what you do at this point, sorry.
Once your tank is cycled you will need to administer fertilizer (Nitrogen, Potassium, Phosphate, Micros, etc.) from time to time for your plants depending on how strong your lights are, what type of plants you have and your CO2 levels.
2. how to prevent algae ( should i use duckweed floating plant) to suck up the extra nutrients
Add pressurized CO2. Raise your light. Use one bulb. Fertilize properly. Don't overfeed fish. Regular water changes (after cycle), all help with algae issues. Telling us more about your particular light fixture, the reflector, the type of bulbs, how it is mounted, light duration along with your fertilizer/CO2 plan will help everyone help you.
3. do i need to alter the lighting setup
See #2 (and advice mentioned by others above).
4. what temp should i set the heating.
78f, 25-26c works for typical tropical freshwater tanks.
Remember to have patience. Iwagumi setups are not built in a day.
P.S - Return those Rams.