1. You can beat both games in 24 Hours if you skip through everything cutscene and dialogue possible though I normally listen to fun parts like dialogue on the Star Forge, Leviathon and Unknown World, HKs and Canderous' dialogue is also fun so I listen.
2. By playing through normal no. But there are many mods that allow you to wear stuff like Darth Revan's Full Armor, Darth Nihilus' Robe, Darth Malak's Armor etc.
3. THere will be many times where you will find youself fighting atleast 10 enemies at once in both games.
4. You can turn good and evil and will change the ending depending on if you go full evil or full light though the first game has a much bigger change in endings.
Hope this helped. Have fun