First step is zoning and asking what they need as well as what it takes to make it happen. Each county is different with its requirements. Mine is like the wild west while the county next to me is a very very different story. I only truly needed permits for driveways/culverts and septic tanks. Everything else is being done by the individual contracting and utility companies. The order of operations would go something like this:
Zoning/permitting
Financing
Grading the area, draining management
Gravel or paved roads
Pads creation
Septics
Water lines
Electric
Internet
Mailboxes
communal areas (laundromats, gazebos, bbq areas, walking tracks, dog parks, playgrounds, etc)
Infil of mobile homes
Where I am from, most of the contractors who do septics can also do most of the rough and finish grading as well as any drainage needs. A civil engineer can help you out immensely. I paid about $2k for my small park but there is another investor I know who paid about 12k in all the design fees associated with it. His park is wayyy bigger, though I can't recall the pad count. Mine was about 20 or so that it was designed for. I wanted some healthy space in between them as well.