The usual cast on a four lot minor split is smaller than it looks. A licensed land surveyor does the boundary work, sets monuments, and draws the plat that gets recorded, and on a clean rural parcel with decent existing deeds that's often in the $3,000 to $6,000 range, more if the old deed calls are vague and they have to chase corners. A soil evaluator or engineer does the septic testing, commonly a few hundred dollars per test hole plus a report. The county charges application and recording fees, frequently a few hundred to a couple thousand depending on the state. A land use attorney is hourly and you use one when there's a title problem, an access easement to write, or covenants to record.
The planner you called is the general contractor over that group. On a simple minor split some people skip the planner and let the surveyor drive it, because surveyors in rural counties file these routinely and know the staff. On anything with a hearing, the planner earns the fee.
What you asked around the edges is the more useful question. This isn't passive. It's project work with a start and an end, and then you're selling lots, which is its own stretch of work. The version that comes closest to what you're describing is selling the finished lots on seller financing so the money arrives monthly after the project is done, and that turns you into a note holder with a whole separate set of rules about who can originate owner-financed paper in your state. Worth a conversation with a real estate attorney before you plan on it rather than after.
