Okay I'm not sure how this situation resolves or if the cards are played in the correct order to activate properly, but here was the situation:

I have 3 ojama tokens and 2 monsters on my field, plus 2 set magic/trap.

My Opponent had 4 set monsters, a face-up messenger Peace and 2 other set magic/traps.

It's my turn; I tribute summon Mobius and target his messenger and 1 of his f/d magic trap.

Now this is where the chain begins, he chains to Mobius effect and responds to his summon, which resolves first?

Order of events: He activates his targeted Ojama Trio then chains his non-targeted Torrential Tribute.

Now when this resolves, he will nuke the field of monsters, lose his Messenger, I'll take 900 damage from the original tokens, and I'll have 3 more ojama tokens on my field correct?

Now I also had a Torrential Tribute set, could I have chained my Torrential after his Torrential and destroyed all the ojama tokens, taken 1800 damage, and both have a clear field, or did I miss the timing for my Torrential?

Actually, you have a chance to respond before he activated his torrential; priority goes back and forth, and you are allowed to respond to his Ojama Trio before he can use his own Torrential. But, the effect will still be the same; unless a torrential was activated BEFORE the Ojama Trio, the field will be cleared and then you will have 3 tokens.

There's one major flaw in that scenario: you cannot activate Ojama Trio if there aren't enough free spaces for the tokens. Since there was 5 monsters on your side of the field, your opponent's Ojama Trio would be an illegal activation, and would be destroyed by Mobius regardless of the fact that Torrential Tribute was activated later in the chain.