You can use blue barb 1h weapons and roll +24 to motw on each, affix level is 82, so item level must be at least that.
But I wouldn't bother since that spell damage is not very useful. Remember if you slap spell damage boost on top of elemental damage you get from armor like jitan, it will add crapload of damage to your skill in character screen, but this damage doesn't work with any ranged aoe attack, only with direct melee single target hit. So that +ele damage added let's say to each projectile from death gaze, or stormblast, or whatever skill you use, it will add only +damage you have on item, not damage*spell power bonus. And if you press A and watch your skill damage there, you see that casting motw boosts your damage by a crapload, this is display bug and doesn't work, it will only work for 1 hit you deal directly with normal attack.
Same goes for minions, they use single target melee attack, so for them it does work. You can give minions nephalem spirit boonus, or necro can give minions DFT totem bonus, and boost them with his burning veil wall, boost them with shadow aura, they gonna deal damage +ele damage from DFT totem multipled by spell power. But for example merc that uses bow skills, it won't deal all that increased damage, despite fact that you see some ridiculous number in "O" menu stats. Same goes for snake stance for example. You can max snake stance + synergy, and put on a poison spell damage gear in every slot. You gonna see ridiculous number like 500k damage thunderslam or something, but it will not deal that damage via any aoe/projectile ability.
You probably know this, but just saying.
I don't use extra buff switch like that because relistically all you get from it is that little +% physical damage it grants, and it is just not worth it, since this build switches to shield/sword quite often to move.
As for titan strike, unlike many other innate skills buff duration works with it. But I don't think it is really worth messing around with, you can just recast it.