Baby number 3 ages gap and gender swaying

This may be a bit longer winded, we’ve just had our second little boy but I know I would like another baby. There is 18 months between my boys. What age gaps do people think is good for baby number 3?

Also I would love to have a little girl, don’t get me wrong I would be happy with another boy but would love a girl. I realise I am lucky to have any babies so please don’t bash. This will be our last baby and I have heard of gender swaying, has anyone used any gender swaying methods that have worked?