One addendum on the actors' deaths
Tim Choate was 49 and Andreas was 59.
RS, CA, and LR take place before Crusade ("Call To Arms" is actually the pilot for Crusade), and occur over the following two years, and the LT takes place 10 years after the fifth season while "Into The Light" takes place 20 years after Season 4.
In a strict chronological sense the spinoffs do go before the final episode of the show; but a lot of it doesn't touch on the same story. "Sleeping in Light" is very specific to the characters in the main 'Babylon 5' show also touching back to several earlier episodes and should be watched directly after "Objects at Rest" IMO.