I don't know that appearance is really important. After all, Pegg looked nothing like Doohan, Saldana sure doesn't look like Nichols, and Cho doesn't look like Takei.
As for accent, it's funny that you mention it since his is real, albeit overly thick.
"He was born Anton Viktorovich Yelchin on March 11, 1989, in Leningrad (now St. Petersburg), Russia, Soviet Union. His father, Viktor Yelchin, and his mother, Irina, were a successful pair of professional figure-skaters in Leningrad, and his grandfather was also a professional sportsman, a soccer player. "
Walter Koenig was of Lithuanian/Jewish descent, hence his original name Koenigsberg.
The Jedi Master
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Back off, man. I'm a scientist.