Grievous:
Kota frustrates Grievous, gives ground and distracting, while Starkiller readies himself to turn the cyborg into a flaming lightning grenade.
Ventress:
Ventress isn't exactly on par with Starkiller on Jar'Kai--who could handle her better than Dooku did--and Kota might stand a chance with TFU1-style.
Darth Maul and Savage Opress:
Maul might be on par in a Jar'Kai fight with Starkiller, but that Force prodigy wouldn't waste time toying with him the way Sidious did. I see Kota nearly on par with Savage in their divided duel, but I see Opress winning as well as Galen did when he was an apprentice, but I also see Opress sacrificing himself again while Maul would be unconscious on the ground, Starkiller having inflicted the same blow of Force Sidious did.
Obi-Wan and Anakin:
I see Kota as an eventual weak-link here, but as displayed in ROTS, Obi-Wan was easily overwhelmed by Dooku's force, and I don't see Starkiller doing any worse a job than the Count at that. Kota would fall to Ani's blade eventually, but with Star's immense Force strength overwhelming Obi and his Jar'Kai overwhelming Ani, I think he wins a really hard fight. His lightsabers move as though their own accord... I used to think Starkiller and Ani were on par in Force and saber, but until TFU2 came my mind changed. And ROTS Anakin didn't use force as much as he did sabers.
Dooku:
Kota falls after a two-minute duel with Starkiller's help, and Starkiller and Dooku's battle of endurance would likely end with Starkiller defeating him the way Anakin did.
Mace Windu:
Kota falls to his overseer and recruiter (Mace) who would likely know how moves inside-out... As for Mace and Starkiller, I think Star would win as capable as Anakin was. Mace was good at Force, but it wouldn't do well in a duel. Mace applies them better in solutions and battlefields. Possible tie for Mace and Star, but... Star's OP.
Yoda:
Kota dies as easily as Anakin would slice him up. Starkiller would eventually be forced into a hard saber fight. Both Yoda and Star are great at focusing their physical might. Yoda did really well against Sidious and Starkiller was very impressive--not to mention, climatic--both in his trailers and ingame. Same answer for Star's eventual duel with Mace. The only reason I think Star would win is because he has more advantages with two blades.