Hiya
STAY VERY, VERY FAR AWAY FROM BRAID FOR TUNA!!
Why:
Braid is very thin and will EASILY cut OFF your fingers or hand. A few commercial tuna guys have lost fingers or parts of their fingers to normal mono fishing line. A novice with braid is definitely looking for trouble.
Braid has almost no stretch, so you will lose more fish due to hook pulls.
Not all rods have eyes that can handle braid. Most roller tips have too big a gap between the roller and its cage, which can cause the braid to get caught up in it. When fishing with braid, you will also need a softer rod, to absorb the shock.
You will also need to spool your reels at a tackle shop with a line spooling station, IF you use braid. It needs to be wound on VERY tight, or else it will just bite into the lower layers and cut itself off when a fish runs.
Braid is VERY expensive. Remember, you'll need anything from 300-600m+ of 50lb braid, PER reel. Much cheaper and safer to simply spool with regular 50lb mono. If you want to save some $$$, buy normal 50lb line and NOT IGFA rated line. Its considerabily cheaper. If replacing line is a issue, bump up your line class to 80lb. You'll be able to fish longer. How-ever, after 2 or 3 good trips, you'll have to change even 80lb line.
Its not a big deal, as most of your fish will be caught on your bait rods. This means that you only need to change the line on your bait rods often, as they will take the most abuse.
Even if my lines have NOT tangled, or NOT touched the boat, or has NOT been damaged, i STILL change my line after a very good trip. I've learnt the hard way of being penny wise and pound foolish.
Keep it simple. Stick with what works, 50lb or 80lb mono........