firstly,
if you are not familiar enough with navegating on open Water out of sight of the Island(when a strong cloud cover comes up surprisingly you can loose visibility to the Isle just a couple miles off) then I would highly recommend that you only go offshore with 2 independendly working/connected GPS. and running with GPS will let you find the FADS always, even if they are not visible on the surface.
the FADs are def the most effective thingy to use for all kinda Fishes, around and under a old/long placed FAD you get it all, the Mahis on the Surface, Wahoos standing close under, and great Bottom Fishing in the Depth there, too.
one spezies brings along an other and an other.
we run here on the southern portion of the East a good number of FADs, some are old, 3 are even willingly placed 15-20ft below the Surface so when the small Mahi Breed is around other Boats do not pass there taking a 50 Mahis of just a couple pounds weight each, as we of course want them to grow up and breed so we can get the real good catches there for a longer while.
Squids are perfect for Bottom Fishing.
as explained in an other post above, they would also be a very effective Surface/Trolling Bait, but they are more difficult to handle and do not serve on the usually higher Billfish Trolling Speeds.
as for Mahis the Squids would be effective but are not necessary, because once you found your rhytm/areas/places to get on the Mahi Schools, they bite on almost everything up there, so the Deadbait Ballyhoos are completely enough to use for trolling on Mahi Mahi.
as for smaller Billfish like white Marlin and the usuallly present smaller Blue Marlin I prefer Ballyhoo much over Squids due the possibility to run a higher trolling Speed. on slow speed below 7 Knots it is not very common to raise groups of 3-6 white Marlin at a Time in the Spread, You need a well thought of Spread for that prepared to run 6-8Knots of trolling Speed.
Ballyhoo are very effective on many Spezies, but it is very important how you get them and prepare them so they would last long enough in the water to be worth to be used.
I get my Ballyhoo Fresh, we freeze them in right away by the dozen per plastic bag, to do so we empty their Bellies from their Poo and we fully salt them. that way you can for example rigg a Dredge with 19 Ballyhoo and leave them in the water for 3-4hrs without any getting bad in that long time in the water.
if you want to target mainly Dolphins/Mahi, check out your area for present FADs and mark their positions in your GPS, on your way to them watch out for Feeding Bird activity in the distance, good markers for present Mahi schools, and run your trolling along the Current Hits/Weedlines, don't fear to get Baits dirty with seaweed, such is usually well worth the bit of extra work to continuously clean baits, those sweet tasting Beasts are right there waiting for you.
let us know what your prefered Spezies are you wish to catch, so we can give more specific advise on Bait preparations, trolling speeds, kind of locations etc.
tight lines
Mike