Can a person make a bracha on a Talis kattan even if later (10-15 or longer minutes) he will make a separate Bracha on a Talis gadol? Is it a Bracha (SHANO TZRICHA) not necessary?
The widespread custom for one who plans to put on a Tallis Gadol, is not to make a bracha on the Tallis Katan he puts on preceding it. One of the concerns is bracha shaino tzricha.
Mishna Brura 8:24, even when there is a substantial break between the 2 and this reason doesn’t apply, see ibid. other reasons for this custom.