I have few questions of making server.

What i can do is JAVA, NodeJS, Python and RDB, NoSQL.

And here goes my questions.

1.What should i keep in mind for first priority when making server? (key performance factor etc)

2.How can i imitate real traffic for performance test? (making bot or any recommended tools?)

3.Is it always recommended for using db connection pool?

4.How many limits would be proper for connection pool?