65 gallons UK is 78 gallons US, so the rough beginner guideline we use would be 78 inches of fish body (fins don't count) as counted up using the maximum expected mature adult size of the given species of fish. This guideline is meant to work mostly for medium small fish in smaller aquariums and breaks down badly with some larger fish, for which you should often have less inches of because they need more room.
The reason you probably won't get a lot of responses is because your question is so big. The topic of "stocking" a fish tank is large and complicated and starts with the unique likes and dislikes of the individual aquarist. The "inch guideline" I've given above is only the "tip of the iceberg" and stocking questions then move on to shoal sizes (many fish need a minimum shoal size) and then to individual species tank shape needs (some fish need height, some fish need very long swimming room) and then on to individual aggressiveness questions and then on to community aggression and then on to changes in behaviour over the lifetime of the fish, such as behaving differently when they get older or drastic changes for mating and rearing of fry.
Whoa, that was a mouthful! Anyway, not meant to put you off, just to get you started thinking in the right direction.