Sea salt is a mineral and so long as anything that is non-kosher is not added to the dry salt crystals the salt is kosher. To say that sea salt is not kosher because non-kosher aquatic life lives in the ocean would be the same as saying that all fruits and vegetables are not kosher because they've come in contact with bugs.
Jewish people treat animals quite well. The Torah forbids cruelty to animals, though does not prescribe vegetarianism.
There are no health disadvantages of only eating Kosher food, though going to a social event with only non-Kosher food would be difficult.
Jewish Germans eat kosher food. Like in other countries though, many products that are sold in grocery markets have kosher certification.
Yes, they must be certified kosher for Passover though.
Yes, tuna is a kosher fish. Canned tuna must be kosher certified though.
No. While kashrut (the laws that dictate whether a food is kosher) has certain rules for what and when certain milk products can be eaten, there is no law that restricts their consumption entirely. In general, there are three rules that pertain to milk consumption: 1) kosher milk is derived entirely from kosher animals and not mixed with the milk from unclean animals; 2) kosher dairy foods (those containing milk) must contain only kosher milk; and 3) milk cannot be prepared or consumed at meat meals.
Yes, it must be certified kosher for Passover though.
The majority of sweetened condensed milks are made with corn syrup and are not certified kosher for Passover. There are substitution recipes though.
Though some brands of granola are kosher for non-Passover use, no granola is kosher for Passover. For Passover, you can get fake 'granola' that is made from matzo. Or, it may be fun to research ingredients and try to make some on your own.
Yes. Fresh vegetables are all kosher for Passover, though Ashkenazi Jews do not eat certain ones, such as corn and legumes (peas, beans, etc.)
Mushrooms are a tricky one - while they're not considered to be animals (despite scientific evidence that they share much more in common with animals than they do with plants), they're notoriously difficult to check for tiny insects that may hide among the gills or in the fleshy part of the mushroom - and insects (with the exception of one type of locust) are most definitely kosher. Therefore, mushrooms must be very carefully and painstakingly examined prior to consumption, and many Jews prefer to avoid them just in case even though they're kosher (the same is true of celery and a variety of vegetables).
Certain types of grasshoppers are technically Kosher, though the tradition as to which they are has been mostly lost. Source: http://www.answers.com/topic/leviticus-11 (Leviticus 11)