The most sheets we have is ususally about 30 to 35 including details and cover sheets with any plat or easement work separate. Even with half the sheets we find it necessary to split the design load meaning that the utilities are designed outside of the model containing the streets and grading. I also like to keep a copy of the existing surface in a separate drawing. I label and explode that surface into polylines and xref this linework into any sheet that needs it. I have a separate drawing the includes all of the Survey information, property boundary, existing easements, deed and adjacent properties. I xref this into a drawing with the subdivision layout and attach it rather than overlay. This prevents accidental modification of these sensitive elements. This layout drawing is then attached by xref to each drawing file. I will also either copy or query the layout linework into the model for design use but the model layers are set to not plot in the individual drawings. Actually I do not xref the model linework into the drawings except for the street profiles and storm profiles if they are made within the model. This allows the layout to be revised when necessary by anyone on the project. The designer working on the model can see any changes through the xref and update that drawing's linework. The separate layout drawing may not be necessary if there is good communication and all of the players have disciplined drafting skills utilizing good layer management. We do not have such luck hence the extra care.
I group my project into the following:
Model - this MAY include the plat, easement documents and cover sheet(s) depending on the project. If separate covers are required, I make a tab in the appropriate drawing file for each
Grading plan and Drainage maps, erosion protection phasing and detention pond tabs
Street plan and profile sheet tabs along with any curb return and cul-de-sac spot elevation details
Storm Sewer plan and profile sheet tabs
Sanitary Sewer plan and profile tabs
Water Distribution plan and profile tabs if required
Detail Sheets as required with tabs for multiple sheets if required.
As I indicated before, if one set needs to be split between multiple users, I just copy the drawing and split the tabs for each.