Matt, when you say the solder was balling up, do you mean it wasn't flowing or the tip wasn't tinning properly? If you've sanded your tip, you've probably removed the iron coating, exposing the copper which will have blackened/oxidised. If so you just won't be able to solder with it. Get some new tips and a little pot of tip tinner. You also need a dampened pad (usually made of natural sponge) to wipe your bit on occasionally. Each time you use your iron, before soldering wipe the tip on the pad and dip it into the tinning pot, and when you've finished, clean the tip and tin it immediately before turning it off. You don't need a variable temp iron, but it's nice to have. A simple, decent 25 to 30W iron will do all small stuff.