I won't get too much into product recommendations, but some general things to consider...
You're going to wind up spending a lot of money on things other than your bicycle. At your size and presumed strength, you may need really good carbon-fiber soled cycling shoes to be able to ride any distance - plastic-soled shoes may be too flexible, which winds up giving you hot spots on your feet. And such a pair of shoes can be $300 or more - and you might need them. I know I do. You simply can't ride any decent amount with shoes that don't fit or that give you hot spots. Shoes that feel great when you walk around in them for three minutes in a store might feel like flaming instruments of torture two hours into a ride. So when you start out make sure the return policy on the shoes you buy is really good - that's one reason good cycling shoes are so expensive - the people who buy them have a really high likelihood of returning them. Once you find shoes that work for you, then you can go bargain hunting.
Or you can just buy a relatively inexpensive pair that seems to fit well, and hope they still work when you wind up doing 80-mile/120-km rides.
The problem is you won't know that you're unable to wear a certain pair of shoes because of hot spots or poor fit on long rides until you actually do long rides.
You may need to play musical saddles before you find a saddle that you can sit on for hours without going numb in certain parts. Good saddles aren't cheap, either. You might need to pay $100 or more for a saddle, because it's the only one you can find that doesn't rub you raw. Literally.
And you may find out what works for shorter rides starts getting really painful on longer rides.
You're going to need things like a good pump (with a pressure gauge!), and if you really want to not spend money in the future the tools needed to maintain your bicycle. Do you really need to spend $50 or more in labor to just change the chain and cassette when they wear out, or to recable your brakes and shifters after a couple of years of riding? You are going to need to changes tires - either to fix a flat or replace a worn-out tire. Park Tool's website has a lot of really good videos on how to work on your bicycle. (At least they did the last time I looked...)
And whatever bike you buy, at your weight the stock wheels will probably need to be replaced as the lightweight wheels that come on most higher-end bicycles won't support you for long. I'd say you need at least a good 32-spoke 3-cross rear wheel with a substantial rim. The front wheel doesn't have to be anywhere near as substantial, but it's hard to get a wheelset that isn't something like 32-hole both front and rear. Google "32-spoke wheelset" for examples. Decent hubs here are important - at your size, you want a steel freehub so the cassette cogs don't cut into it, so I'd say get a wheelset that has Shimano hubs, such as 105 hubs. You don't need to pay for a hub with a titanium freehub, and you want to stay far, far away from any hub with an aluminum freehub.
So don't blow all your budget on your bicycle. (FWIW, IMO 105 is the "sweet spot" for Shimano groupsets - I race on that. It's plenty good. Ultegra is basically 105 with a different finish and a few grams shaved off. DuraAce is overkill, IMO, even though it's really nice. As is electronic shifting - yeah, it's great and really shifts well. But it won't get you in better shape nor make you faster. Don't worry about paying extra to shave grams off your bicycle until you can ride a cat 4 pack off your wheel in a USA Cycling sanctioned race. And if you seriously get into triathlons you're going to need a whole other bicycle anyway...)
When you start, don't set a distance goal - just ride to how you're feeling. 30 miles may be months away, depending on your current level of fitness. Once you get started, it's not too hard to figure it out.
You may want to get a heart-rate monitor so you can track your effort and your fitness. FWIW, if you do, you should probably also get one with GPS, so you can record your rides. You can start with a phone app to do this, but beware, as using your phone for that can drain your battery fast, so it's not good if you ever get up to doing four or five hour rides or longer.
And be prepared to face growing pains - the second and third week are probably going to be tough. You'll probably go through phases such as
- Phase 1 - Hey, it's raining out, I get to skip my ride! :-)
- Phase 2 - Hey, it's raining out, I'm gonna get wet! :-(
- Phase 3 - Hey, it's raining out, it'll keep me cool! :-)
- Phase 4 - Hey, it's raining out. Been there, done that, I'm riding the trainer.
Don't be afraid to take a day or two off here and there. You will need to recover at times. A good sign of this is your legs being sore day after day and you can't seem to get any stronger/faster (OK, that's really deep into overtraining when that happens, but I suspect you'll probably drive yourself into that pretty quickly...)
And get a compact 50/34 crankset. You'll appreciate the extra low gearing when climbing at your weight. And I don't care how strong you are, you can't spin out a 50-11 gear combination anyway, so you really can't make use of the bigger gears a standard 53/39 crankset gives you.