I am sorry to hear about the loss of your cat. The loss of a beloved fur buddy can be quite devastating, to say the least. I am glad to see that you have a new fur baby in the home, and that you are deeply involved in research into what makes a healthy, and happy cat. SCM has supplied a couple of excellent websites to browse and her statement is pretty well on the money for what you should consider when it comes to striving to raise a healthy animal.
One of my male cats years ago suffered from urinary tract problems. I was fortunate enough to catch it and take him to emergency at 12 o'clock midnight some 2 hours away from home. In discussing the problem, the vet asked where the litter box was, and I said in the basement. She then said I was extremely lucky to have caught the problem in the early-stage with the litter box so far away from the living area. She recommended, would you believe, a quiet area in the kitchen or in the bathroom if it was close to the main living area of the house where the cat's movements could be observed by people but not disturbed too much. I have followed that rule for 10 years, and in that time there have been several times it has paid off with some of the others having urinary tract issues.
As far as hard food for the cat's teeth go about the best on the market is raw chicken necks. I'll pick up chicken necks at the butcher's bring them home, and cut them in half or in thirds and freeze them - 2 or 3 times a week I'll give a piece as a treat after thawing it out. Put it in a plastic bag, and place it in hot water to bring it up to body temperature before giving it to the cat. DO NOT USE A MICROWAVE. It will start a cooking action as soon as turned on destroying the natural nutritional value of the neck along with making the bones brittle, and causing a digestion problem
A wee bit of seafood from time to time as a treat should not cause any problems. When it is used as a mainstay this can cause issues, and anchovy should be avoided even in fish oil supplements. It is known to be a microtoxin to cats and depending on the cat and the length of time administered can possibly cause a problem.
I am enclosing a couple of websites that I have found useful in the past, and still refer to even today. Hopefully all the information in these different websites that have been mentioned will be of value in the raising of your new fur buddy.
Any further questions, just let us all know.