When looking for Unity shmup templates, I came across this great set of posts on the Shmup-dev website. One post includes an excellent talk on unity shmup development, with slides and source code to go along with it. It really touches on some of the basics and key points for creating a shmup, including performance considerations. Object pooling is absolutely necessary when creating a high performance game, and the author monoRAIL explains it very neatly for readers.
C# template (mine)