Can I ignore importance, adjoint equations, GRDFs for my path tracer?
No, you don't need to know this stuff to implement basic path tracer.

Basic unidirectional path tracer is quite simple to implement. Just trace bunch of paths of length X for each pixel with uniform distribution over the normal oriented hemisphere at the path's intersection points. Then weight the remaining path with the BRDF at each intersection point and multiply with luminance of light once the path hits a light.

You'll get quite a noisy (but unbiased!) image even for large number of paths and then you can start to look into methods to reduce noise, e.g. importance sampling &amp; bidirectional path tracing. Just validate the more optimized path tracers towards earlier validated path tracers to avoid introducing accidental bias.