I would add more ratchet binders, up around 10. These seem pretty good:
http://www.amazon.com/Security-Quikb.../dp/B002IY20AE
You need a strap winder as well. Four pipe stakes (30" high) are pretty much a requirement. I would go with some shorter chains. I have:
- 6 x 6'
- 8 x 16'
- 8 x 25'
The 25 foot chain rarely gets used, but it seems like when I need them I end up using all 8. I would have at least 20 straps. Don't forget to get a couple of 40 foot straps too, or even a 50 foot especially with a step deck. Mostly for loads that need to be belly wrapped.
I would also add 4 30 foot 2" straps and 4 portable strap ratchets. Lots of loads need this type of stuff. Polystyrene insulation comes to mind. Make sure you have two winch pipes at all times, you may break one, or you could get one stuck in one of the snap binders (I've done it) and the only way to get it out is with another winch bar.
I assume that the trailer comes with two load levelers and a few portable chain tiedowns?
You'll also need some way to wrap up the snap binders. Kinedyne makes these small things that work really well, see if I can find a link. Or you can just use bungees. The snap binders are required to be wrapped in something as to prevent them from snapping open. It can happen.