Note - AWS will always keep an unreserved concurrency pool with a minimum of 100 concurrent execution to process the requests of the functions which didn't set any specific limit. So you would be able to allocate up to 900 only.
A Balance Between Memory and Execution Time
Performance - Cold Start vs Warm Start
You will notice in every blog or documentation mentioning that Lambda execution environment already does have AWS SDK for Nodejs and Python so don't add them in your dependency. It is good for performance improvement but there is a catch. This SDK library will be upgrading regularly with the latest patches and may impact your Lambda behavior so prefer to have your own dependeny management.