Aww crap- I knew you would ask me how much line!!! That’s what I get for opening my big yap… Off the top of my head, I can’t remember how much PP is on the reel.
However, this is how I set up most of my trolling rigs:
Typically you usually run more than one rod of the same type, right? 2 or more downriggers, dipsies, planer boards, and so on. Starting with an empty reel, reel all of your PP onto it( 150yd. spool of 50/12 would work great) Then, tie on whatever backing you choose( usually 17lb. mono for me) to the PP and spool that line onto the reel to fill it up.
I use line counters exclusively, so this is the part where it helps. Tie that mono from the first reel to the second reel. Clear the counter on reel #2. Spool all backing from #1 onto #2. Make note of what the counter says on reel #2 once all backing is on, and finish spooling #2.
You now have one fully spooled reel(#2). Spool on the same amount of mono onto reel #1, tie on PP, spool that up and tada!!
I know it was awfully wordy, sorry, it the best way I could explain it. I hope it helps.