There's a time known as the Republic Dark Ages, when the Republic, for all intents and purposes, ceased to exist as a body with any political clout. More and more territory was overseen by Jedi baronial rulers and the Republic was pretty much just Coruscant and the core worlds.

To answer, no I don't think Mandoa culture is agreeable. Aside from Traviss' mary-suing of the Mandalorians, they exist in a state of permenant war and preparedness for war. It's been shown before that if they don't have a good enough Mandalore or conflict to unite behind, they scatter to individual clans. Furthermore, their state of permenant aggressiveness has never really endeared them to the Republic at large. Most viewed the Mandalorians like early europeans viewed the Vikings. You tried your best to appease them or **** of the way of the war du jor. The problem I see is that Mandalorian culture has no way to really exist properly in times of peace. They're supposed to die in glorious or honorable combat. That leads to insanely high rates of attrition as Mandos aren't known for retreating, no matter how suicidal the odds are.

Well... I've always viewed Sith Philosophy as kind of a weird hybrid between Randian Objectivism and the Ubermenschen ideal. A Sith is supposed to act with utter enlightened Self-interest, doing only things that benefit themselves in both the short and long term. The Sith that go lightsaber-killingspree-happy are failures. They act with no consideration to their future power base or generation of loyal servants who will aid their ascent to being top dog. The end goal of is this is 'freedom'. This is not the freedom to act purely on impulse and whim, but the freedom to no longer be constrained by morality as others define it. You redefine morality and reality around you via your absolute strength of Will and determination. The reason Sith disdain weakness or for example, helping others is simple. If you continually help others, you weaken them. They come to rely upon you instead of pulling themselves up and finding their own inner strength. This is why the Sith detest the Jedi, seeing them as doing nothing but breeding weakness and decay, creating a galaxy that -needs- the Jedi Order to solve their problems or fix the catastrophe of the day.

Iridonian or Colony Zabrak? The general rule is "Iridonians are the warriors, Colony Zabrak are the Explorers". If you're looking for a culture to use as a basis, I'd suggest the Maori or possibly even the Norse, who were both famed warriors and explorers.

That and ruling a galaxy of smoking husks wouldn't be that impressive.

I honestly like what TCW did with the Mandalorians. It reduced them from being a Planet of Hats (Hat being mercs/warriors) into a more nuanced culture that had internal disagreements. The New Mandalorians kinda had a point too, considering the Mando way of warfare was "Start strong, lose horribly once the Jedi come".

The answer to any question asking 'who do we call to beat x' is always Kyle Katarn.

I forgot to mention that Traviss was notoriously....protective of her work, to the point of publicly and viciously lashing out at anyone who critiqued her. If you want to read some good SW books that aren't too reliant on Force Users being kickass, I recommend Timothy Zahn's work. He manages to make normal folk interesting without going too hard on making them living gods.

Well..... The Republic Commando books were good, I'll give her that. The problem is that eventually the books turned into a tug-of-war between Traviss and the other writers on which faction was more super kewl leet. At one point, her Mandos had lightsaber immune armor and were completely immune to the Force when they wanted to be. They were also portrayed as simply being absolutely perfect, that the Mandos were the absolute epitome of everything. They were the best warriors, pilots, commanders and even farmers.

There's a small problem, but not a big one. Zeltrons are very emotional, yes...but they swing to the extremes of the emotional spectrum. An angry Zeltron is an out of control berserker and a sad Zeltron is the world's biggest emo kid (sorry for that analogy). That COULD be overcome and could also present an interesting RP situation. How would Tasha keep herself from being utterly consumed by her rage to the point where she's a mindless beast?

It means getting cut down by my lightsaber.

Kudos on mentioning that being a Sith isn't being a kill-happy lunatic. Besides, a Sith who just randomly walked around Kaas City butchering people for the hell of it would be 'taken care of' very quickly.

Because the Empire promised the Mandolorians a glorious war.

It really depends. A Sith could rise to Darth via political manipulations, assassinating their rivals, doing something that benefits the Empire, leading successful military campaigns or even plain old nepotism. Being a Darth doesn't make you the supreme ****** Sith though. You still have to answer to the Dark Council

It's a combination of Baras' supreme arrogance and paranoia working actively against him. That late into his life, I have a feeling Baras was jumping at shadows and killing anything that even had the potential to be a threat to him, regardless of its loyalty or not