On the 744, the N1 has to be at or near idle, as well as the main gear untilted, before the reverser locks unlock. Having the engines spooled up at touchdown actually delays reverser deployment.
Not quite - on the 747 the gear tilt has to set "Weight on Wheels" (WoW - which is based on gear tilt) true before the reversers can be deployed. But there is no N1 logic in the reverser controls on the -400. At some point the actuators may have difficulty in overcoming the aero loads, but you'd need to be well above idle before that came into play.
The 747-8 does have N1 logic that would prevent reverser deployment with N1 too high (structural reasons), but it's quite high (~75% N1 IIRC) and would only be expected to come into play during an RTO.