Question about off season

You could do a combination of the two - substitute the long runs from the half-mary plan for the long runs in the tri plan.

Year before last I trained for a Oly and a marathon at the same time and that's what I did for the long runs and it worked fine for me, and despite being VERY slow at the marathon, I still felt good and well prepared for it.

I'd find a relatively low volume ('beginner') 1/2M plan and schedule some swimming and biking around it.  The 'low volume' recommendation is not because you want to swim and bike also, but because you appear to be a relative beginner -- can't tell since there are no logs to see.

The reasoning here (in my own mind, at least), is that once you get to the race, the swimming and biking that you did are not going to mean much.  If you haven't prepped the run properly, the fact that you can swim 2 miles in an hour means little to nothing, unless you plan to swim for part of the 1/2M.  So do the 1/2M plan to be sure that you've prepared for the run, and any swimming and biking that you do are gravy on top of that.  Nice for keeping the body lean and the internal systems (heart, lungs, metabolism) 'go', but not much else, I think.