At a first glance, 3-5 figures is tough limitation, but when you start to think about it there are loads of potential games. I eas quite intrigued by your question and I often find inspiration in movies or books and there you can find many scenes that can provide a potential small wargame:
-Wild West gunfight
-Samurai
-Three musketeers
-Pirates
-Gangster shoot-out
-Gladiators
-Snipers(WW1/WW2)
-Napoleonic (Sharpe)
Etc
Another avenue could be historical situations involving a few characters. My favourites here are encounters where kings or famous leaders personally were involved in combat and the outcome could have a significant impact on the course of history:
-Gustavus Adolphus fell at Lutzen 1632
-Charles X almost killed at Warzaw 1656
-Louis Napoleon killed by Zulus 1879
-Richard III died fighting at Bosworth 1485
-Vlad the Impaler killed fighting Turks 1476
Etc
For miniatures I would go for 40mm if available for the action chosen
Please post your game once you decided and good luck with your project
