I just transformed my 35g FW
First off let me say that my tank was not running for about 5 months but still had all the gravel and everything else in it. I cleaned the tank and sold the gravel.
Locally Live rock runs $9 a pound but I found some on kijiji for $4 and bought the necessary 40lbs. I kept the tank alive while I biult up a fair bit of money for the equipment needed. I did so by mixing a salt water and running a bubbler on each end of the tank because the live rock needs water flow to stay alive as well as heating the water. I then purchased the sand and added that to the tank. After waiting a few days for the sand to settle I filled the tank and began placing the live rock. After that I added the HoB
protein skimmer (buy a good one its the backbone of your tank) a better light (not necessary) and 2 powerheads. There is some debate as to how much water movement you need but I would go for a minimum of 10x flow. Buy 2 powerheads with different gph
rates and point them at each other and at the surface. The surface agitation will oygenise the water and the direction till cause lots of water movement.
I then added 2 hermit crabs an made sure they lived for a few days before buying my first fish. Add them slowly about 1 every week or 2.
Make sure you have a good test kit and test at least every second day for salinity, ammonia, nitrites and nitrates.
Edit: Oh and dont use your current filter. It is not needed if you have enough live rock and flow as it could lead to high nitrates if not very well maintained.