The license cost is about $180 with a minimum of 20 user licenses for D365 F&O. (USA)

Depends on the modules and the processes to be implemented. Timelines are influenced by the process that needs to be implemented , what %age is fit and what percentage is a gap. Size of the organization and the number of users.

Not really , it all depends on what are the needs of the organization and how best can we leverage the existing functionality. The implementation and consulting charges usually remains flat across ERP , more the customization, migration and training requirement more will be the cost operation and maintenance cost.

It is always recommended to use professional assistance . This will avoid unwanted delay and unnecessary costs.

Changing the old habits is something that is very important during the implementation. Lack of flexibility , integrations needed from other applications  are some of the challenges .

The four main modules are:

Finance
Commerce
Supply Chain Management
Human Resources

Finance: The Financial module can be used to perform numerous financial business processes. Some of the sub modules in the Finance module are are Accounts payable, Accounts receivable, Budgeting, Cash and bank management, Compliance, Cost accounting, Fixed assets, General ledger, Project management, Public sector and Regional regulatory features.

Commerce: The Commerce module has retail management functionalities which can be used to manage the commercial business processes in the organization. Some of the sub modules in the Commerce module : Call center, Channel setup and management, MPOS and Cloud POS, Commerce developer and administration.

Supply Chain Management: The Supply Chain Management module has a complete view of inventory, warehouse, manufacturing, service, and logistics with data insights which help the organization to make better strategic decisions. Some of the sub modules in the Supply Chain Management module include cost management, inventory management, Master planning, Procurement and sourcing, Product information management, Production control, Sales and marketing, Transportation management and Warehouse management.

Human Resources: The Human resources module can be used to automate and optimize many of your human resource processes. Some of the sub modules in the Human Resources module are : benefits, employee development and training, questionnaire, recruiting and payroll.