There is absolutely no problem in taking your tea with C4 - there isn't any real interaction between them, and if stims are what got you concerned here, tea is minimally stimulant, so it will not make such a difference. The same goes for the sugar, I see no problem in taking a bit of sugar before working out - a bit of fast acting energy is always good for that. However, I would not use milk, as it can neutralize many of the ingredients found in C4, making them useless. Therefore, just take a sweet tea and C4 before working out, and you will be fine.