I agree with Bester's order, with a couple of differences - see below - and also agree with his strong recommendation
not to watch "In the Beginning" until much later - between series 4 and 5 works (when it was made, in fact) - for the reason he said: it spoils many aspects of the ongoing series, otherwise.
The differences:
(1) The film "Thirdspace" slots in, chronologically *, after episode 8 of series 4 ("The Illusion of Truth"), though because it was made at the end of series 4 there is no reference to it in the remainder of series 4 after episode 8 (which would seem strange, as it's about a `significant` event).
(2) Chronologically, "The Legend of the Rangers" comes before "A Call to Arms" (though it was made later).
(3) If you really wanted to be chronological about your watching (some do, some don't), you'd save the very last episode of all (the last of series 5), "Sleeping in Light", until after everything else, including "Crusade" and "The Lost Tales".
(* Strictly speaking, the film "Thirdspace" fits, chronologically, after the first act/teaser of episode 9 in series 4 (a certain person's new uniform fitting) and before the rest of that episode, but that might be taking the desire to watch things chronologically a bit too far
.)
