No Export for You: For a long time, this was the status quo and there was a reason: the logistics seemed impossible, especially the longer time went on. Let's break it down:
Even discounting the side-stories, there are one hundred and ten episodes to dub into English or even just subtitle (which, discounting the OP/ED portions, still amounts to something on the order of thirty-six continuous hours of material), and realistically good sales in the pre-streaming era would've been thought to require dubbing; if dubbed, there would be at least dozens if not hundreds of actors to recruit, quality of footage and transfer would have to be ensured for all the material, if dubbed the entire soundtrack would have to be re-layered into the English track (again, thirty-six hours of such), and then the distribution company would have to distribute a product that is roughly equal in length to the first three seasons of Battlestar Galactica combined. It might have been possible had the series been released in America roughly coequal to the Japanese releases, but by the turn of the millennium, outside of a television deal (for a series which contained animation that was 20+ years old) with advertising support, any kind of domestic release was completely impossible. An OVA-style release of the sort other TV or OVA shows got in the Anglophone market would've been a similar kind of suicide, even at five episodes per disc: five episodes/disc at, say, $30, would still equal a twenty-two disc set that would cost the consumer six hundred and sixty dollars. The only real way it was ever going to happen would've been some kind of miracle deal with SyFy or Cartoon Network (or someone similar), and with that not coming, an Anglophone release just wasn't possible - not due to any apathy or maliciousness on the part of anyone on either side of the Pacific, but just from the sheer scale of the undertaking.
The hobbyist fansubbers who subbed LoGH with the highest dedication and quality themselves took years to complete it - the final episode of the second Gaiden series was released in September 2010. The first season of the main series had been completed in 2003. Anyone attempting to translate LoGH faces an absurdly Herculean task.
The advent of the era of streaming, however, finally opened a road for distributing the show in English without crushing the bank. The original show went live for streaming on June 20th, 2017 as a lead-up to the 2017 reimagined version. (It's still worth noting it took Sentai two years from initial acquisition to releasing the show.)
The Other Darrin: Hozumi Goda replaced Kei Tomiyama as Yang during his last appearances following Tomiyama's sudden death from pancreatic cancer.
Talking to Himself: Mostly averted. Even guest characters or one-shot characters are often voiced by a voice actor unique to that character. In one example, the notoriously laconic Ernst Eisenbach spoke only one word on screen. He was voiced by actor Masane Tsukayama who had no other role in the series. By the end of the original series' run, almost every living Japanese voice actor had voiced at least one character on the series.