What are the primary goals of creating a building model? Who are the key stakeholders?

• What do they need? They need a space that optimizes the small square footage for research and accessibility. The stakeholders are the researchers and any visitors that come by.
• What do they care about most? Research space, storage space, solar capacity, solar retention, lab space, work space and accessibility.

How much detail should you include in your building model? How do you decide?

• As you develop your initial design?
• As you continue to iterate and develop on your design?
• What are the key stages?
• And how much detail should you include at each stage?

How much detail should you include about the composition (layers, materials, thicknesses) of your wall, floor, and roof assemblies at different stages of your design process?

• Conceptual design
• Preliminary design
• Design development
• Construction documentation

Many door and window manufacturers provide Revit families for doors and windows that you can specify for your building design.

• What is the advantage to manufacturers for providing these families? (it's not free to create and provide them...) They get their product advertised such that when they are constructed the models can be used in reality. Greater chance of business. Also they can see how their product interacts with others.
• What is the benefit to you as the designer of using these manufacturer-provided families? Is there an advantage to using them versus the families provided in the Revit library? The data that are provided are up to standard and most likely accurate.

What are the advantages of getting the Revit component families (for furniture, equipment, and fittings) directly from the manufacturer versus from an online sharing website like RevitCity.com?

The chance for error is lower, as they have a higher standard for qualifications. The pieces in Revit are also built to code regulations such that the models you create is compliant and "ready-to-go".