Actually, Fighters have the best Saving Throws in the game( especially if they are Dwarves). Paladins are good too, thanks to their innate bonus. You may refer to SixOfSpades' online website for a comprehensive coverage of the various classes' Saving Throws tables.
Additionally, Minsc is a Ranger, and a Human one at that. He levels up slower than a Fighter, and thus his Saving Throws in the early beginning are pretty abysmal; but he will eventually have good Saving Throws( they peak at Lvl-21).
For a Fighter/Thief combination, if you want to go the route of one hit, one kill; you may entertain the thought of an Assassin->Fighter dual. However, this is not an easy dual to pull off if you are not comfortable with the game mechanics.
Kensai->Thief is certainly feasible, especially if you wield a Quarterstaff around, but Katanas are fine too. They have excellent backstabs thanks to their Kai ability which ensures maximum damage with each hit( barring Criticals).
The Berserker->Thief is the easiest to pull off, and one of the hardier ones around thanks to the Berserker's Rage ability.
The Wizard Slayer->Thief path is an unusual one, but with proper items equipped, you can easily abuse the game by making him into the Ultimate Tank. Healing from damage taken is possible with him, while having 100%+ Magic Resistance. Not easy to pull off though.
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As for reactivation of abilities, as I said before, you can easily postpone many quests for completion later.
Cheers.