I plan to fly from MCO to NRT (via IAH). According to the itinerary, only 54-min for transit time in IAH. Is it enough???
<Is it enough???>
It's 100% possible to go from Terminal E (or C) arrival gates - to Terminal D (ANA) departure gate - in 54 minutes. It's possible to walk or use the Skyway (elevated tram located airside) if needed and go from gate to gate in 5-10 minutes max. The problem is that this leaves very little margin for delays - for whatever reason. If it takes too long after landing to get to your gate, or to deboard the plane, or whatever reason - this shaves off connection time. Don't dawdle, don't stop, get to your gate first - your plane will be boarding already - Good Luck!
As always, bk_t1 is spot on. I do hope this is a protected connection?
Yes, do not detour along the way!
Well that depend on the time of the year you are flying. Spring can have lots of weather delays and that 54 may kill you. Otherwise, its enough time except of flights delays.