Hi, Otter! Welcome aboard Rebreather World! It is a great community!
As for the question of how to approach trimix, I started on OC trimix, and went to CCR's.
From that stand-point, I would have to say that the hard part, as most folks will agree, is the OC to CCR transition. Once you get over that hump, the rest is just normal stuff. So, having done it the wrong way, using my hindsight (15/15) I would have to recommend that you go to CCR's, and do your trimix training that way! There really isn't a lot of reason to do it once, and then do it again. You already know how to breathe on a regulator, all you have to do is learn your deco techniques, and gas mixes. Doing a hang on a CCR is nicer from the standpoint that the gas is at least warm and moist!
Rob