You shouldn't eat too much candy. It's not good for you.
Don't eat too many snacks. They're bad for you.
1) You shouldn't eat too much candy. It's not good for you.
「キャンディーの食べすぎは良くないよ。」
このキャンディーは飴のことを総称して言っているので、単数形になります。
2) Don't eat too many snacks. They're bad for you.
「お菓子食べすぎると良くないよ。」
「お菓子」は snacks や甘いものなら sweets と言えます。
ご参考になれば幸いです!