Permissions to be granted to developers to investigate jobs, queries, and packages
Don't grant ssis_admin if the dev shouldn't be sysadmins:


  Members of the db_ssisadmin role and the dc_admin role may be able to elevate their privileges to sysadmin. 


Source: https://msdn.microsoft.com/en-us/library/ms141053.aspx

Personally I would never let the devs create jobs with their accounts. As soon as they leave the company and someone disables the AD account, all their jobs stop working...

Btw: don't grant server rights directly but with a serverrole.