having read the OP and skimmed most afterward i would say you are likely get the basics from the pinned topics (nice job, someone actually read the pinned topics) and the other comments here.
what i would add is that your questions on tankmates are generally unnecessary when they can be answered with one simple blanket statement (in this case) : no, don't try any of those combinations, they are ill-advised, will not or are highly likely to not work long-term, and can pose threats to the gar or other fishes. period.
more details:
Cubans are aggressive gars and the silver fish rule generally applies here (even if the silver fish has some bars or bands or whatever mottled pattern to it). some bichirs can work with gars better than others (similar size is best) and other gars often work best. knife fish are hit or miss. definitely not advised (or wise) to go with pbass, nile perch or any of the other non-true perches (and even true perch are not advised). gars are best kept with other gars of similar size, a few bichirs work, and SAL/AUL can work. if the CBG is your centerpiece, do what you can to keep all the fishes happy in that environment. good luck--
--SRD
PS-- CBGs are sensitive to pH fluctuations and water quality moreso than other gar species, you will have that to keep you busy instead of dealing with poor tankmate choices--