Pretty much. 'In the Beginning' is easily the best of the bunch, though if you have any intention of checking out Crusade too, then you'll want to watch 'A Call to Arms' as it's a quasi pilot/bridging movie.
'Thirdsapce' & 'River of Souls' had their moments, but you're not really missing all that much by skipping them. 'Legends of the Rangers' is a bit of an odd duck as while it's technically a movie, it's really just a feature length pilot for a series that didn't get picked up. It's not great (I mean imagine if 'The Gathering' was all we saw of B5!) but there are elements that work...and some that don't. Mostly it's the last time we ever got to see G'Kar before Andreas Katsulas passed. So there's that.
'Lost Tales'....well it's not great, but half of it is at least half-way interesting...I guess? Again, it's another one of those things that was meant to be a first instalment in a series that never happened.
Basically B5 has shite luck when it comes to spin-offs. So another thing it was doing way before NuBSG.