The big difference with normoxic trimix will be a greater END and depths to 200' on O2 mixes down to 18%. As you noted, the learning curve won't be steep.
I agree with your assessment that advanced wreck would be more pulling than finning techniques. While I am admittedly biased, you can tell the difference between wreck divers who trained on wrecks and cave divers who transition to wrecks - cave divers tend to dive with greater precision and tend to more conservation focused, and they look better in the water, in terms of both skills and configuration.
My thoughts are that Cavern and Intro to Cave will get you the farthest in the least amount of time while acquiring the fewest bad habits.
Cavern will teach you/demand excellent buoyancy and fin techniques that will directly translate to wreck diving - and with greater potential to explore the wreck without silting it out. The line skills are basically the same - a penetration on a primary reel, with the major differences being how you do ties offs and placements - and running the reel is about the same, the difference will be the focus on running the line with minimum contact and silting. Intro extend the pentration beyond the ligth zone and begins to solidify all the skills you need to truly deal with an emergancy without being dependent on the need to surface or even go shallower. (Full Cave does not add much in terms of basic skills but adds complex navigation in overhead environments and usually brings deco into the picture.)
That you would be missing would be training in the various hazards unique to wrecks, but that is mostly academic and easily picked up without the need for advanced wreck once you have the essential skills learned in Cavern and Intro out of the way.
What may also be missing will be various deco techniques related to various sea conditions, and with careful wreck/enviornment selection in normoxic trimix, you'll pick all that up in that course.
So....if it were me, I'd do Cavern and Intro as a single 4 day course, and no offense to IANTD, but I would do it through an NACD or NSS-CDS instructor in N FL. Then build some experience and get comfortable at penetration diving at depths in the 100-130 ft range before complicating it by going deeper. Deeper = a lot less time. And that has an impact in temrs of both the time you have to deal with an emergency but also the time you have in the water on any given dive. For example, on a 150' wreck you'll have maybe 30-40 minutes on the actual wreck and the rest of the time will be hanging on deco doing basically nothing. In a 60-100' deep cave, you can do a 2 hour dive doing and learning for 90% of that time with maybe 10 minutes of deco. Plus you almost never get blown out - it's rare for all of the N FL caves to be blown out, and you can do 2-3 dives per day without having to be on the boat at 6am and you save a tone in boat fees that can be directly put into more diving.
In any case, once that is out of the way, you can do normoxic trimix and after building some experience at deeper depths, go on to the full trimix course.
To be fair, there is a significant risk with this approach - you will potentially discover that cave diving beats the hell out of wreck diving and you will become addicted to cave diving.
As an aside, deco in a cave environment is different in that you don't control the overhead and cave profile and the penetration is not a 200-300 ft but rather 2000-3000 ft. Consequently, if you experience a failure or problem on a deep wreck you have the option to abort on the spot, ascend more or less immediately and start your deco. In a cave, that will most likely not be an option and while you can turn early, you are committed to the ceiling imposed by the cave to exit. It creates a different mind set, but one that is heavy on planning, anticipating and preventing problems and developing a thorough understanding of the comples factors that have to be managed if something goes wrong as immediately beginning your ascent is not an option. That all translates very well to thorough planning and redundancy on a wreck.
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In terms of your goals, the Luistania is deep, but is iin a mud pudde compared to Iron Bottom Sound. There are a few wrecks at diver accessible depths, but the really cool stuff is measured in thousands of feet of depth. Chuk and Bikini however would be exremely interesting. Saipan also has some superb shore diving as well as several seldom visited wrecks.
