We have a deployment team that does the implementation of Salesforce Commerce Cloud. In corporations, you have your OS upgrades along with that, you have all your installations being upgraded. Whether you have Microsoft, Salesforce, or Oracle, it's a very smooth process. You don't have to wait for updates and walk up to your IT manager or IT team for help. This has never happened, the maintenance is smooth.

I was part of the team that did the implementation.

A vendor team implemented it.

I'd recommend having skills in-house or getting a technical PM as a sounding board, so you can challenge system integrators.

We completed the implementation in-house. 

Whether we follow an implementation plan depends on the client's requirements; however, the initial setup is the same.

If they want to launch their campaigns, personalize their merchandise, help shoppers find what they want and if they want to boost organic traffic, again, it depends on person to person and from client to client.

In our team, we have 5 people involved in the use and implementation of salesforce, including managers, developers and administrators. Implementation can take up to 2 months. 

We did it in-house.