Extra roost space is not a problem. The chickens seem to enjoy having more options, and in hot weather it is really nice if they can spread out to stay cool better.
If it is bigger than the current brooder, it is an improvement!
Honestly, I would not consider a run "necessary" at all with that amount of space, that many chickens, and the style of coop you showed.
More space is always nice, and of course it would be good to add more run space as soon as you can, but the chickens should be fine until you do.