Adding swimming into the mix...best approach?

First I'd say don't get so wrapped up in getting all of those workouts in that you forget to take rest days.  Especially just starting out that's a good way to get overtrained and burned out really fast.  2 workouts in each discipline per week gives you that rest day, even if you don't brick them.

There's also no rule that says every week's workouts have to be the same.  Feel free to alternate swim-intensive and bike/run-intensive weeks.

For swimming, you might see if there are any local Masters swimming workouts that work for you.  While you should probably emphasize your weaker sports where you've got the most potential for improvement, it's not really a good idea to ignore any of them and you want to hang onto the advantage you get from your strong swim.

You might want to look at some of the workoutplans here on BT to see how they have them split. For the most part it is two workouts a day which you can do morning/evening, morning/lunch, lunch evening , whatever works with your schedule. Like the previous poster, i do one workout in the morning and one after work, that is what works for me. I don't think you want to add so many brick workouts in a week, especially if you are just starting out.