Will a standard SQS that I configured to invoke a lambda when it receives message invoke "many lambdas" or only 1 lambda at a time?
From Using AWS Lambda with Amazon SQS:
Lambda polls the queue and invokes your function synchronously with an event that contains queue messages.
It will invoke as many as required, depending on your reserved concurrency limits:
Lambda increases the number of processes that are reading batches by up to 60 more instances per minute. The maximum number of batches that can be processed simultaneously by an event source mapping is 1000.