Hi, I'm new here but I'm not new to Reef Keeping. The first few things you will need in order to convert to a FOWLR tank are as follows:
Refractometer.
Don't waste your money on inaccurate swing arm or float style salinity contraptions, you'll end up buying a refractometer anyway. Well worth the extra money.
Live rock.
For 100 gallons buy as much as you can because it does most of the filtering. Its expensive so look for deals in the various buy/sell forums online. There's always some one shutting down a tank.
Flow.
As mentioned above, you need at least 4x more flow in a salt tank.
Filteration.
You should be able to get by with your cannister filter for now but ditch the filter media and just use it for carbon. Save up your money in order to buy a good protien skimmer, don't waste your money on the cheep ones, again, you'll end up buying the more expensive ones in the future anyway.
These are just my opinions but I hope it helps.
Danny