Hey, Jason,
On another thread, I think it was the "Recommendations, please" , forum member John Jedinak said he had extra copies of Guillow's "How to build" booklet. He said he would give a copy to anyone who needs it. The booklet has very good, easy to follow, information. See if you can round up a copy. The Don Ross book is really informative, goes into much detail about flying the models, too.
The green rubber in the kits is not good for anything, as far as I'm concerned. I got 3 flights from it, wound to only 75 turns.
Tan rubber is just fine. There are several sources online. Google: free flight model supplies that will get you started.
How much and what size? There are varying opinions about this. You could wait and read Don Ross' book, it's in there.
I think I mentioned this before but, I'll say it again..... get your model balanced according to the plans and get it to glide properly. First.