Whether a Thinkpad has soldered RAM or not is model-by-model thing. When I was laptop shopping I tried to stick to the only non-soldered ones, but they are definitely more expensive, as they are the higher-end models. I absolutely cannot wait for CAMM to, if it ever does, become a normal thing for RAM modules.
Old Scratch is another name for the devil, so Linux From Scratch sounds like a winner (loser?)