To say it in a specific number is not part of the Sunnah. You may offer your salutation as many as you want but without restricting it to a number. The best on is the longest on which is known as al salawatul Ibraheemiyah

Sheikh, salawath means which we say salam to prophet (sal) . Which is best salam to say. ( Allahumma salli ala muhammed) There are lots of ways said in books. Some are very long.And we used to say 100 times 1000times like that.is it ok?