By the sound of it, the biggest sawfile you can find! Make sure it is a sawfile, though, and not an engineer's threesquare. You need the rounded bottom to the gullets that a sawfile leaves to avoid the possibility of cracks developing in the metal, which can happen at sharp internal corners, which the threesquare will leave.
On set, the usual advice is as little as you can get away with. Set to give a kerf little wider than the blade is thick to start with, say about 50% wider, especially if the blade is taper ground. The less waste you have to remove the easier the saw will be to use, especially for any length of time. If the saw doesn't like minimum set, you can always increase it a bit, but squeezing metal back the other way once it's been bent one way may result in teeth breaking off. Try to set just the tips of the teeth rather than bending the whole tooth as well, so that subsequent jointings and sharpenings will take you back to unbent metal.
Try it and see - that's the best bet.
Edit to add - a bit of rake on the teeth will help a lot. I had a new ripsaw that had no rake at all, and it kept jamming in the cut - far too aggressive. Somewhere between 5 and 10 degrees of rake seems to work much better.
