IIRC, you can use the special abilites of the ki focus or the flaming staff, but not both at the same time. You could certainly change the damage type to fire, but when you hit, you'd either get the +x bonus from the weapon (meaning you did not use your ki focus, and thus cannot use a power with implement keyword), or use the +x from the ki focus (implement keyword powers). It sounds confusing, but it's not really.
For adding flavor to a character, you can always add Themes from Dragon 399. The fighter has found religion? He can take the Ordained Priest theme (
Dungeons & Dragons Roleplaying Game Official Home Page), giving him a spalsh of divine without expending a feat to multiclass. Themes grant an additional encounter power, new features at 1st, 5th, and 10th lvls typically, and allow the player to optionally choose theme specific powers (usually utility powers) throughout heroic tier in place of one of thier normal utility power choices.
You don't have to take a theme during character creation, taking one as the story progresses if you want, but they mostly represent part of your char's background. You can swap out themes during retraining after gaining a level, provided you don't have any feats or powers that require your existing theme.
In my Eberron game, I allow players 1 theme from either Dark Sun if they are generic enough to not be tied to Dark Sun, or from the Dra399 themes.
Dra399 themes:
Alchemist (Arcane/Artificer-ish)
Animal Master (Ranger-ish)
Chevalier (Knight/Paladin-ish)
Explorer (Ranger-ish)
Guardian (Defender-ish)
Guttersnipe (Rogue-ish)
Hospitaler (Divine/Leader-ish)
Mercenary (Fighter/striker-ish)
Noble (Warlord-ish)
Ordained Priest (Divine-ish)
Order Adept (Arcane-ish)
Outlaw (Rogue-ish)
Scholar (Bard-ish)
Seer (Arcane-ish)
Wizard's Apprenctie (Arcane-ish)