I know in the indie license you don’t have access to unity’s shader library, but can you use your own? If not, can you use your own in the pro version?
Unity has access to the same shaders as Unity Pro, there is no difference between the two.
There are just shaders that won’t work with Unity (basically all that require Render Textures like shadow, replacement, reflection and refraction)
Nice. Do we have access to RTT with the indie version (for post processing for instance)?
As I mentioned above, no. Render Textures are only accessable to Unity Pro (Unity Indie btw does no longer exist, only Unity 
)