"...so I guess weight of bottle could be an issue?
Not unless you purchased lead bottles.
Aluminum anodized, stainless steel, polymer...even if your touring bike carried four bottles the weight of those four empties would not vary much across the spectrum of materials. Now, fill them and calculate the empty weight as a percentage of what you aboard your fully loaded touring rig weigh. It's a fairly insignificant number.
Just go BPA-free or stainless and if you are going to carry white gas or such for your camp stove get a Sigg fuel bottle anodized in a color that will keep you from accidentally taking a swig from your Sigg.
And one last point, despite all the hoopla about BPA in plastic food ware, no human has ever been proved to have been harmed by it. Now...lab rats feed 500 grams of BPA per day... If you get out on the open road and need to replace a bottle use the old sailor's advice, "Any port in time of storm.".