Laceecal,
I typically chose my fire poi head by weight. Some people prefer one style of knot or fold over another. All styles feel pretty equal to me when spun, besides the weight.
As far as handles and chains go, they are more of a personal preference. As long as they are from HoP, you know that they are top quality and safe to use.
My first fire poi was
http://www.homeofpoi.com/shop/productDetails/Pair-of-Medium-Cathedral-Ball-Chain-Fire-PoiCheap, safe, durable, groovy and I still play with them after more than a year of service.
Remember when looking at the weight, the described mass is with dry kevlar. Saturated in fuel the heads can be much heavier as I am sure you know.
Have fun! Everything is going to work out and we will all hold hands, dancing, singing, and enjoying our brief moment in space and time
Love,
Sean