What are the limitations of Add-Ons? What are the API Limits as per editions in Vtiger CRM? What are the limitations of Automation? What are the limitations of Customizations? What are the limitations of Document Collaboration? What are the limitations of Email Functionality? What are the limitations of Marketing Automation? What are the limitations of Storage? What are the limitations of Support Management? What are the limitations of Tasks & Calendar? What are the limitations of User & Access Control? What are the different editions available in Vtiger CRM? What is Sales Starter and Sales Professional? Are there any limitations based on editions? What are the key features of Vtiger CRM?