I've been longarming for quite some time now. Knowing what I know now, I'd recommend a set of circles and a good straight edge. This will get you started and there's almost nothing you can't do with these tools. There are other tools you may like as you get further into quilting, speciality templates/rulers, etc., but they aren't necessary in the beginning for sure. The circles can be used for anything not-straight, and the straight edge (preferably about 8-12" ) for everything else. Then you can see if you need more, or not. Unless you're going to do only freehand (with no outlining/SID) or only pantos, you will use these tools, so they won't be wasted money. On the circles, I find the solid circles easier to use than the rings without the centers - they tend to pop up and are harder to get hand placement correct...although you can learn how :)
Anyway, just my thoughts...and have fun!
Debbie in Austin