5k workout: what should the rest be?

Yes, about 1:1 for this type if workout.

At "goal pace" the recovery should be relatively short, a jog of one quarter the distance of the fast interval just completed. If you're hoping to string all these fast sections together in a race then the recovery must be minimal.

1x1600 @goal pace, jog 400
2x800 @ goal pace, jog 200
4x400 @ goal pace, jog 100

those distances work out to right around 1:1 so I should be in the ball park.

lol. maybe walking rest

For 5k workouts, I usually do roughly a 3:2 work to rest ratio, but I jog the recoveries.

I usually end up running pretty much spot on what I do in a race, e.g 5 x 1k w/2' jog recovery - ends up bang on race pace.

If you're doing a static or walk recovery, you could likely do a 2:1 - or perhaps even less rest.