I think the key thing to remember here is that any given reader is only interested in how to install one particular configuration. They are not interested in learning about all the other systems it could be installed on.
The other important factor is whether the reader has to make any decisions about which pieces to install or where to install them. In other words, is there a planning process that has to take place before the actual installation process takes place. If there is, it is a distinct process and should be documented as such. In the planning process, the reader does need to know all the options available and the questions they have to answer to decide which ones to install.
Once those decisions are made, they want a simple straightforward install procedure for just the options they have chosen.
The decision points are part of the planning documentation, not part of the install documentation. For installation, you want a separate install procedure for each of the possible outcomes of the planning process. (Depending on the number of options involved, this may need to be generated dynamically.
Each procedure should clearly identify which decision path it belongs to and direct the use back to the planning topic if they are not sure they are in the right place.