"b) Your (2) is faulty. I agree that there is no guarantee that our sense impressions are correct (there is the possibility of error), but you need sense impressions to have any coherent knowledge of the world. If you treat your sense impressions as undefined, then you must treat all of your knowledge as undefined"
Regarding sense impressions and their place in the assembly of information...
It goes beyond whether the sense impressions are accurately perceived. Sense impressions are nothing without context and interpretation. Sense impressions are broken down differently for different uses.
A painter re-assembles visual reality without having to know the chemical make-up of things...except the paint.
Similarly, persons have explained the world based on their sense impressions without knowing the chemical makeup of it...or the time span, or the actual history.
However, once you know the air is fulled whose atoms with fewer protons and neutrons than those lying around on the ground, you can look at the world and see this. You can train yourself to see what you know to be true to the latest scientific findings. (When someone asks my 'race', I am tempted to tell them more about DNA.) Of course, there is a hazard in thinking of the light in your day as electromagnetic fields propagated from far away...and of our hearts as a muscle that pumps...since in the far future we might discover that light is spiritual and the heart is important in "fondness."
But we can "see" things as modern science understands them...with a little training.
Error also enters when we don't follow the rules for that particular application. For example, it is an error to leave food to rot(and it smells)
UNLESS we did so on purpose -- for example, in a compost heap or for the purpose of making a time lapse film about food rotting.
So I better go have dinner now. I'm called.