What is a platt map? I looked up the property lines and codes pertaining to zoning and setback prior to purchase.
Did you happen to read the bit about short of explosives!"?
Plats are not a substitute for a survey. The dimensions on a plat are estimated, not actual.
If the grading and wall you envision don't come close to the boundary line of your property, you're probably fine. However, you cannot encroach even an inch across the boundary. If you do, you are at the mercy of your neighbor. Had a friend make that mistake with a deck extension project. Deck had to be torn down and rebuilt.
If the neighbor is your cousin or your mother, no big deal, you buy the land you encroached on for $1 and have the property boundaries redrawn. Otherwise, you have to hope your neighbor will be kindhearted and give you an easement. Depends on the neighbor. If you've been shaking his house and knocking his pictures off the walls for weeks, he might not be in a giving mood.
Think it all through carefully before you put your plan in motion, and maximize your communication with the neighbor. Most people will be far more helpful when you include them in your planning process. Make sure you listen to their concerns ahead of time and try to address them before the first shovel hits the dirt.