I will be taking my first tech diving courses in about another year, but would like to get the gear I will need together so I don’t' have to purchase it all at once.
Makes sense. As several posters have mentioned, there is a certain logic to pursuing some initial training - either a GUE fundies course, or just speaking with 1-2 tech instructors - before you start buying much gear, to get some informational background as you pursue purchases. Maybe what we can help most with is some general reassurance as you start down the path to ever more exciting, or financially ruinous, diving. My two general recommendations:
1) Don't spend too much time trying to buy the one and only one 'perfect' or 'exactly right' rig. And, don't let a lot of people (like me, and others) second guess your choices after you make them. You can narrow things down to a certain degree - you want a BP/W rather than a soft back BC, or you want larger steel tanks for backgas rather than AL80s. But, sooner or later, you just have to take the plunge - bad pun, I know, but applicable - and get in the water with a rig, and start tweaking it.
2) What you buy first may be ideal at the time you buy it, but your interests and 'tastes' and preferences will evolve. Few people buy and use forever one and only one set of 'tech' gear. What I was sure I liked 6 years ago, and what fitted my needs as I started technical training, is not necessarily what I prefer now in all cases. But, I made the right choices then.
Your post doesn't identify what your current rig is, so some suggestions may miss the mark. But, as TS&M and DevonDiver point out, you will definitely need a backplate, harness, and wing. (Of course, the wing you use for single tank diving will NOT be the wing you will use for doubles diving.) You will want some good, reasonably stiff, paddle fins. For that matter, you will want a good exposure suit that fits you well. I suggest in particular that you configure your single tank reg with a long (7') primary hose, and a short hose, bungeed necklace alternate, and get used to diving that. It is an inexpensive equipment modification, but you will need to be proficient with it as you pursue technical training. DevonDiver provided the longer term 'wish kist' of gear that most tech divers find is necessary. As he and others said, you can start with some relatively inexpensive basics first.
What BCD recommendations? I have been told Halcyon is the best, but pricey. ... If Halcyon is the safest, then I'll pay the money.
Halcyon supplies great gear, and I dive several Halycon wings (and some other Halcyon accessories). But, I also dive Dive Rite and Oxycheq wings, and OMS backplates, etc - i.e. I do not personally see advantage (or disadvantage, either) to having a 'single brand' rig (I also happen to buy a lot of used gear). Nor would I say that Halcyon, or Dive Rite / OMS / Oxycheq / Zeagle / whatever is 'safest'. Don't focus on the brand as much as the performance specifications for what you will be using in your initial training / diving (which is why the recommendation to talk first to a potential instructor is useful).
What regulator recommendations? I rarely do cold water, mostly I dive in NC and FL.
Cold water isn't quite as much an issue as breathability at depth. Most regulators you might select for deeper diving will also handle colder water. And, there are a substantial number of excellent regulator brands, with the choice an individual makes being influenced by factors such as 1) what is locally serviceable, 2) what other divers that you may end up in the water with during training are using, or 3) what an instructor may use and recommend, etc. Within most regulator brands there are models providing different levels of performance, and it is hard to say that a top line Apeks is 'better' than a top line Scubapro, or a top line Zeagle, etc. I happen to dive Apeks (and Zeagle) regs, but my dive buddy uses ScubaPro, another tech diving buddy uses Posiedon, I have rented a couple of Dive Rites for some deep deco dives (after gear was stolen on a trip to FL), and we are all happy with what we dive.
What type of tanks are recommend? LP or HP? ... I was thinking either double HP100s or double HP117, but would like to consider the LP option if it is better.
You will get diverse recommendations on tanks, which also reflect what individuals happen to be using. For example, I dive HP steels, and therefore recommend HP tanks, while others who routinely use LP tanks might give a different perspective. There are quite a few SB threads on that subject and I encourage you to review as many as possible. In NC you might find HP tanks a little more available in local shops but that is a relatively trivial matter. Double HP100s are really nice tanks - I have a set myself. But, there are many who suggest if you are going to get HP100s. go ahead and get HP119s, or even HP130s, to provide more gas. I have a set of each as well (and my favorite set of doubles for recreational diving happens to be double AL80s). I presume that you are a young, and very physically fit, Marine and the weight of a set of 119s or 130s wouldn't be an issue. But, my primary point is that there are quite a few options, and not only one correct option. At your height, the only option I would probably stay away from would be double HP120s. But, beyond that ...