To get rubber, put sticky resin in a squeezer and pipe the resultant Latex into (a/several) coagulator(s). Then combine the resultant rubber chips in a crucible or extruder to get rubber sheets.
The first goal of GT6 is to get one or more thermometers, however they take steel, so before then you just have to calculate/guess.
The Google sheet Gregtech_crucible_Shared can help calculate the amount of fuel required for a batch.
K, went back and took a look. I see the squeezer, not too bad. Need to make a boiler then a steam engine to run the machine. The next problem is the coagulator. From what I can tell you have to make stainless steel to make that. So what I'm seeing here, is there is quite a while where you are using the crucible without thermometer or hazmat suit. Is that correct?