It's pretty self contained, one of the advantages of old made-for-tv-reruns media.

Being able to identify the characters might help some, but otherwise no. It's a two part capsule episode

Not really. It's not part of ds9's big arc. Little bottle time travel episodes. Guess knowing that the Romulan's have lent Starfleet a cloaking device for the Defiant might help you not get into a canon mess over some of the technobable reasons for the time travel.

I'm not sure, but the basic set-up is DS9 is a space station positioned near a planet wherein one species has very recently freed itself from slavery to another species. It's in the ass-end of nowhere and is seemingly a quiet posting until a wormhole leading to the unexplored gamma quadrant opens nearby, drawing all kinds of attention. That's all I really remember and it's probably largely inaccurate, lol.

It's a time travel episode, so no, not really.