You certainly have made an excellent choice. I have been doing tuna trips with Viking since the 1980's and I can say that they are an incredibly professional and courteous team. A definite key is to read the party boat tuna fishing do's and dont's thread:
It is a must for party boat tuna fishing and it is chock full of valuable information.
For tackle, I bring the following:
-2 Stand up rods with 50 class reels filled with 80lb test (I have had too many malfunctions, breakoffs and tangles causing huge loss of line, etc. to rely upon only one rod during a hot bite)
-1 jiggging rod with a Saltigs 40TT reel for jigging
-1 rod capable of deep dropping for squid with heavy weight for when the squid are not on the surface
-1 lighter rod with a bait casting reel for casting for mahi on the surface
-1 very light spinner for casting squid jigs
-A quality fighting belt
-I pre-tie all of my baitfishing rigs with 80 and 60 pound test
-I have a few jigs with pre-tied leaders as well
-For mahi, I bring a mix of spros and softbaits
-I also bring an assortment of trolling lures but Viking maintains a healthy set of their own so you need not bring any unless you are as compulsive as I am.
The above list is probably overkill - I could probably get away with using half of what I have listed but I actually enjoy prepping for a trip almost as much as going on one.
All that being said, I will be on that trip as well - feel free to PM me if you want to discuss anything further.