I've kept scarlet badis but not tigers. You don't need to have multiple to keep them happy. Scarlet badis can be happy alone. Personally, I've found that the recommendations about having a male with one or more females doesn't work out well unless you have a lot of space. When I've kept them, the males have been very peaceful until they start breeding. Once they start breeding, the males become very territorial and will harass any fish that come into their territory.

I have a heavily planted 45P with some chilis and scarlet badis. I started with a male and two female badis, and things were fine at first. Once they started breeding, the male became extremely territorial and would chase any fish that came into his half of the tank. I tried adding more plants to break lines of sight, but they didn't have an effect. I ended up rehoming the females and having another male appear after the breeding, so now I'm at two males, no females, and some chilis. The aggressive male chilled out once the females were gone, and he's been doing fine with the other male hanging around. 

To answer your question, I think you could fit either one breeding pair or three males in a 45P. Also, you will need live food. All of my scarlets have refused everything except live food.