For recreational users, you need to "inform" ATC when/where you'll be flying if you're inside the 5-mile perimeter. Notice I say "inform", not "seek permission", as technically the tower folks can't prohibit you from flying there. If they do, then the assumption of risk is much higher for you, since they told you not to, but by law, they can't prohibit you from flying there.
The 400 feet is again a FAA recommendation, not a law per se. Legally, the FAA is prohibited from regulating the flight of recreational UAS's, so they can only provide the altitude limit as a safety guideline, not a regulation.
Read contacting guidelines here:
Contacting Airports: Hobby vs. Commercial Drone Requirements
Read about FAA requirements here:
Fly for Fun under the Special Rule for Model Aircraft
Here's the special rule related to recreational drone use:
SEC. 336. SPECIAL RULE FOR MODEL AIRCRAFT. (a) IN GENERAL.—Notwithstanding any other provision of law relating to the incorporation of unmanned aircraft systems into Federal Aviation Administration plans and policies, including this subtitle, the Administrator of the Federal Aviation Administration may not promulgate any rule or regulation regarding a model aircraft, or an aircraft being developed as a model aircraft, if— (1) the aircraft is flown strictly for hobby or recreational use; (2) the aircraft is operated in accordance with a communitybased set of safety guidelines and within the programming of a nationwide community-based organization; (3) the aircraft is limited to not more than 55 pounds unless otherwise certified through a design, construction, inspection, flight test, and operational safety program administered by a community-based organization; (4) the aircraft is operated in a manner that does not interfere with and gives way to any manned aircraft; and (5) when flown within 5 miles of an airport, the operator of the aircraft provides the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport) with prior notice of the operation (model aircraft operators flying from a permanent location within 5 miles of an airport should establish a mutually-agreed upon operating procedure with the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport)). (b) STATUTORY CONSTRUCTION.—Nothing in this section shall be construed to limit the authority of the Administrator to pursue enforcement action against persons operating model aircraft who endanger the safety of the national airspace system. (c) MODEL AIRCRAFT DEFINED.—In this section, the term ‘‘model aircraft’’ means an unmanned aircraft that is— (1) capable of sustained flight in the atmosphere; H. R. 658—68 (2) flown within visual line of sight of the person operating the aircraft; and (3) flown for hobby or recreational purposes.
