Geez, it’s not like these guys are unknowns. Orlando Bloom is the only member of the cast without significant experience; everyone else is an accomplished Hollywood veteran with multiple credits and extensive work experience in Hollywood:
ELIJAH WOOD has been one of the hardest working actors in show business, appearing in movies nonstop since 1989 or so. He has, by my count, two dozen film credits and at least half a dozen starring roles aside from Frofo.
SEAN ASTIN has been in Hollywood productions since, what, 1983? He has been in one movie after another, including starring turns in “Rudy,” “The Goonies,” and “LOTR,” plus supporting roles in 35-40 films, including some really good movies like “Bulworth,” and “Courage Under Fire.”
DOMINIC MONAGHAN, as already said, is an accomplished TV star.
BILLY BOYD is the least accomplished actor outside Bloom, but he’s been in stage forever and already has a big role in the next Russell Crowe epic.
IAN MCKELLEN is, of course, an Oscar-nominated actor of immense talent and fame.
VIGGO MORTENSON has had a number of big roles in one major productions after another; “Witness,” “28 Days,” “Psycho,” “A Walk On the Moon,” “G.I. Jane,” “A Perfect Murder,” and many others. Over 30 film credits.
JOHN RHYS-DAVIES had his own series, “Sliders,” which sucked but it was very popular, and has been in more movies than most people have watched. He was, of course, in “Raiders of the lost Ark.” “Asps. Very dangerous… you go first!”
LIV TYLER is of course one of the most beautiful women in Hollywood, so she’ll never lack for acting jobs; she’s also a pretty good actress, and has been in many films. In fact, since 1995 or so she’s been one of the hardest working actresses in the business. Somehow managed to be Steven Tyler’s daughter without coming out all mangled and stuff.
CHRISTOPHER LEE has been in more movies than anyone alive, IIRC.
CATE BLANCHETT is a Hollywood veteran with many leading roles and an Oscar nomination.
HUGO WEAVING was, of course, Agent Smith in “The Matrix,” so if you question his acting chops, he’ll go all kung-fu on your ass.
Even the lesser roles are all staffed by experienced professionals: Miranda Otto’s a very accomplished actress, Sean Bean has been in many films and TV series, Brad Dourif has scores of movies on his resume, Bernard Hill’s been in a zillion movies, Andy Serkis has been in 15 movies in the last 5 years, David Wenham has been working very hard in many films, and Ian Holm is a very successful actor with several leading roles.
When you think about it, really, Jackson went to some trouble to get generally very experienced and skilled actors. He cast only one novice in the whole cast, that being Orlando Bloom; even small roles like Bilbo are filled with top-notch professionals. Contrast that with Star Wars, where all three principles were pretty much unknown. It would have been easy to plop cheap newbies into these roles, but he got mostly veterans. These people have been working steady for years; why would that stop now?
As to the height issue:
Elijah Wood: 5’7"
Sean Astin: 5’5"
Dominic Monaghan: 5’6"
Billy Boyd: 5’7"
Sylvester Stallone: 5’8"
Dustin Hoffman: 5’5"
Michael J. Fox: 5’4"
Billy Crystal: 5’8"
Tom Cruise: 5’7"
Kevin Pollak: 5’6"
Mike Myers: 5’7"
Al Pacino: 5’6"
Robert De Niro: 5’9"
Robin Williams: 5’8"
Matt Damon is 5’11" or so: I think he looks short because he’s stockier than most actors and Ben Affleck is REALLY tall.
Mel Gibson looks really short to me, but claims to be 5’11".
But anyway, it doesn’t look like you need height to be a star.