Salt is good if he ever has fin rot or the like. 16 oz is way not big enough. You can get a cheap tank at wally world,5 gallons for like 10 bucks. Or even a 10 gallon for the about the same. Some of us use critter tanks like from petsmart or petco,ranging from a gallon to 4.5 gallons.
Bettas come from warm tropical waters,so they need heat. Around 78-80 degrees. So you definetly need a heater (unless your house is warm) and a thermometer.
Not to be mean,but you shouldve really done research before getting a fish.