Once you are in PCT, the goal is to allow your body to begin producing test on it's own. HCG will act at a primer, to help "turn the engine over" once you come off. If you never stop the HCG, you don't give your body a chance to produce on it's own. At some point, you need to stop, and the best time is right before PCT starts

HCG though cycle will reduce the chance of getting atrophy of the testes and will force your body to continue producing. You want the testes to stay as full in size as possible, to allow you to produce the max amount of hormone and you want to keep your body used to producing test, when it would normally shut down, on cycle. 

As for clomid and nolvadex, You can run Clomid and Nolva together. You can run either alone. I prefer nolva over clomid. Clomid can cause some uncomfortable emotional side effects. It makes me and a lot of other guys feel like they are on their period. Not a good time lol. I see a lot of guys taking tons of SERMs in PCT and I don't think over doing it is going to make you recover any "better" or faster. You have to remember that these are powerful drugs, not to mention, they are designed for females with cancer. These drugs have side effects. You want to take enough to get the desired effect, but you don't want to over do them