Questions about Streetpass Mii Plaza DLC

Now that I have Find Mii 2 unlocked, I am considering to buy all the DLC for 15 dollars, but I have 2 questions:

1. Does it matter if the people you streetpass have the DLC?

2. Whats the 5th open slot for?
I see Plaza, Puzzle Swap, Find Mii 1 & 2, then 5 blank spaces. I know the DLC will take up 4, but what about the 5th?

1). If the person has the DLC it can change what you do with them. In Mii Force, and Monster Manor, they do nothing different. However, in Warrior's Way, you have the chance to potentially gain many more warriors to use from them, as their army size will be larger than soneone who does not have the game. (For the regular people, you recieve the number of total different people they have in their plaza, which is like 20. D: ).
Flower Town let's you see their favorite garden, which is kinda pointless.
So it really doesn't matter, unless you want to use other's armies to increase yours.
2). Across the top then bottom, left to right they go:
[Plaza] [Puzzle Swap] [Find Mii] [Go To Plaza Gate]
[Mii Force] [Flower Town] [Warrior's Way] [Monster Manor]

The, [Go To Plaza Gate] is for when you have the plaza open and streetpass someone; and let's you greet them without closing the 3DS.

@Clayton Thank you, I'll buy them tomorrow. I have 2 streetpasses in my plaza, but I'm waiting until I get my same people everyday 2-4 streetpasses. One of the two currently in my plaza was a streetpass on the road, another was from a McDonald's Nintendo Zone. I'd rather use 6 streetpasses at once than 4 personally.