The parameters already exist in ffbonded.itp because the CGenFF server version is older (4.0) than what we provide in the CHARMM36 port (4.1). Delete the lines in the .prm file that cause the parameter clash.
Yes, you need to deal with all of it. Angles can (in principle) be overridden, which is why it's a warning. Type 9 dihedrals are the sum of multiple terms, and is an error because when there are non-continuous blocks of parameters, that will produce undesired behavior.