I love 60 degree triangles.
I would not prewash anything. The Best Press won't care, and by not prewashing you can take advantage of the starch/sizing that's already in the fabric. However, I also love the crinkly look after a quilt is washed; if you don't like that look, then prewash it all and put it in the dryer to shrink.
I've never had any luck finding spray starch in a grocery store or Walmart in western Canada, but I did find it once at my local dollar store (on clearance for 25 cents! I wish I had bought it all!). I find inhaling the spray starch unpleasant, so I prefer Best Press. I usually just use Best Press now, since I can find it, and it does a good job. I spray it fairly liberally, and let it soak in for a bit before ironing. I have also made triangle quilts without starching; it's certainly doable, but starching is much easier.
When joining triangles I find leaders and enders very useful. Those pointy corners can really get mangled otherwise.
My favourite 60° ruler is the Creative Grids one, which has the tip cut off. If you're only using triangles it doesn't matter, but if you're connecting the triangles to other shapes like diamonds or hexagons, the cut-off tip makes aligning the pieces easier. I actually made my first triangle quilt just using the 60° line on my 6x24" ruler, so whatever you have/choose will be fine.
Like Prism said, try not to overhandle your pieces; those bias edges will start to stretch and fray eventually, even if you starch your fabric to cardboard stiffness.