Hello. Thank you for coming to JustAnswer with your question, and welcome.
The U.S.D.A. classifies intake of fish oil up to 3 grams (or 3000mg) daily is generally safe. However, most people take less than half of that dose. High doses of fish oils may not be safe for a number of reasons, the most concerning of which is the increased risk of bleeding and hemorrhagic stroke. And you are correct, there can be other adverse reactions from high doses long term. So I would advise that you stay with a normal dosage, which would be recommended on the label of the fish oil you purchase.
The amount of water is good. But your water should be taken over the course of the day, not in large batches. Drinking all or most of it before dinner is OK also, especially if you are inclined to need to get up at night to urinate often.
I am also concerned about the idea of eating raw fish. Generally, this is not considered safe. Even Sushi chefs are stringently trained in the preparation of raw fish before it is eaten. There is just too much of a risk of parasite infection, or bacterial infection. Fish and seafood is very good for you, and properly cooked, it is better for you than raw.
You are correct to be concerned about calcium in your diet. You need calcium to control blood pressure. If you are not going to take your supplements, you will need to compensate with dietary sources for both calcium/magnesium and vitamin D.
You need grains in your diet (it looks like you are aware of the need to avoid anything with gluten), for the vitamin and mineral content they contain. I would disagree with not eating grains. You should have about 3-4 servings of grain each day, preferably whole.
Generally, to control blood pressure better, you need to reduce your weight if you are overweight. Drastically reduce the sodium in your diet to less than 1500mg. Eat mostly whole grains, vegetables and fruits with small (or no) amounts of red meat, a little more of chicken and fish, and legumes at least twice a week instead of meat.
The idea is to reduce the fats, sugars and sodium in your diet. You should have no more than 3-5 serving of fat (one serving is about 4.5 grams or 1 teaspoon of oil), and this fat should be the "good" kind, such as olive oil, or vegetable oils. Sugars should not exceed 75 calories per day (1 teaspoon of sugar has 16 calories). And as I mentioned, sodium should be kept under 1500mg. Eating fresh foods you prepare yourself helps you maintain this level. Otherwise, carefully check food labels and serving sizes.
This has been proven to work to control blood pressure better than anything else, along with some physical activity every day, adhering to your medicine regimen, and regular check-ups by your physician.
As for arthritis, there are a number of causes. The most common is "wear and tear" over time of the cartilage in the joints. Weight loss and physical activity as much as you can tolerate are the best help for this. Many people also take a Glucosamine, Chondroitin, MSM supplement and swear that it helps. Some research has concluded that this supplement is beneficial, and is generally well tolerated by most people. Keep in mind, however that glucosamine can also increase the risk of bleeding, so if you are taking this supplement with fish oil be sure not to go over the recommended amounts on the labels.
Here is a very good tool that can help you: Mayo Clinic Healthy Weight Pyramid Tool
Just fill in some information about yourself, along with whether you want to maintain your weight, or lose weight, and it will give you the amount of each food group you need to eat. You can also print out a 4 page document that lists the amounts of different foods in each group.
Also this site: CalorieKing.com is free to use, and you can look up just about any food you can think of for nutritional information that includes fats, sugars, and sodium. (along with other information). It is very easy to use and very handy when you are trying to control sodium in your diet.
Your nutritionist is correct about one thing. If you treat your body right, it will have a better ability to heal itself. But cutting out essential foods, is not the way to go. Also, some foods in their raw state are good. Many fruits and vegetables are very wholesome when eaten raw. Some however, need a little cooking. Examples would be tomatoes and spinach. They are nutritious raw, but will actually give your more if cooked a bit. And meat/fish of any kind needs cooking for safety's sake.