Is it okay to rinse mouth with water several times immediately after brushing or it will minimise the benefits of toothpaste?

No. Rinsing your mouth after brushing will not negate the effects of brushing. Use floss as well for optimum care. Have a healthy diet, exercise 30 minutes/day, drink plenty of water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV and Covid vaccines. Wish you good health!

You have to rinse after brushing to eliminate the materials brushed from your teeth and any loose particles in mouth. It is normal and the toothpaste already has done it's job. Also floss and massage gums and rinse again if you whish.

Rinse of your mouth with non fluoridation liquid for example water might reduce the amount of the tooth paste ‘s anti cavity effectiveness.

You only need a pea-sized portion of t'paste. Brush w soft t'brush for 2 full minutes by the clock. Spit out remaining t'paste or rinse once or twice. But most adult tooth decay and gum disease starts between teeth, where t'brush can't reach. so you must floss or WaterPik daily. Ingredients in t'paste can't penetrate a layer of plaque (mostly bacteria). And see Dentist regularly.