Yes, this sentence is correct: Ich bin zu dick, dabei esse ich schon weniger Süßigkeiten. = I am too thick/fat, although I already eat less sweets. "dabei" has different meanings: dabei = though, although dabei = in doing so, while (Ich gucke einen Film. Dabei esse ich Chips.) dabei = "with somebody/ something" (suggested sentence above: Ich habe mein Handy immer dabei. oder: Wir sind dabei! = "We are on it.")

I don't see anything wrong with it.

I dont think dabei would be correct here. You would wabt to use "deshalb". In that case, yes, you can have a sentence afterwords. I think dabei means "to have with". For example "Ich habe mein Handy immer dabei".

ich bin Mohamed