Pond Pioneer,
Sharks as a whole are really not
difficult to care for. They need a lot of space, and heavy filtration. Of course, that's speaking in general - there are certain species that would be considered difficult, as they just don't adapt to captivity very well.
I'm assuming by blacktip shark, you mean blacktip reef sharks - there's a pretty big difference between the two. Blacktip reef sharks are extremely common in public and large private aquariums (as far as the ORV sharks go, anyways), and reach about 5 feet. They're pretty well-adapted to captivity, and do well provided they are given enough space. Blacktip sharks, on the other hand, get in the 6 to 7 foot range, and rarely survive in captivity. They're high-strung, and even in the largest systems they seem to not survive very well.
As far as a setup, again - it's really nothing that difficult, and doesn't even need to be that complicated. Start with an above ground pool, add insulation on the entirety of the inside. Then add a pond liner, preferably two. Weigh that down, or find a way to get it to stay tight. For filtration, I would run a pair of large bead filters and a large skimmer. Learn how large skimmers work, and you can build your own for cheap. The bead/sand/cartridge filters can be built too, but it's usually similar in cost to just buy them (use ones made for pools, they're pretty cheap). Use a few large pumps to run everything, have one flow into some kind of bio tower and gravity-feed back into the tank. The others can return directly to the pond, and be used for additional flow. Heating can be done a number of ways, an inline heating system is probably the easiest and cheapest, though.
I would add some kind of lid to that setup (at least some kind of netting, if not something more solid), as well as a few large storage tanks to store/mix water for water changes. But that's a pretty bare bones shark setup. You could do that for around $10K, and house most of the ORV species.
That $10K doesn't cover most of your costs, though. You've got to feed them, which will be a few hundred a month, if not a week. If you live near the coast - easy to catch your own food supply. If not, get ready to pay thousands a year in feeding costs. Animal costs are expensive too - you're not going to get a BTR for under $2,000. Whitetips are similar in price, and atlantic ORVs are typically a little bit less than that. Water changes will be much less frequent, but when you do them they're still going to be big. You can cut down on salt costs by doing a DIY mix, but again - another thing that's going to take up time, space, and money.
As far as tank sizes, most people throw numbers out there without knowing what they're talking about. BTRs should ideally be kept in something that is, at MINIMUM, 36 feet long by 12 feet wide. When keeping elasmobranchii, minimum isn't really recommended. Ideally, they would be in a pool in the 45' by 15' range. That would be suitable for 2-3 BTR for life. As far as depth, it's similar to keeping other fish - make sure they're not out of the water, and give them at least some room to swim vertically. But, 3-4 feet deep is sufficient.
You can keep these sharks in round pools, as well. However, I personally don't recommend it to people. Unless they are MASSIVE pools, they encourage the shark to constantly make turns, which can cause deformities and overall isn't the healthiest thing for the fish. They really need the distance to swim, and longer oval-shaped pools are often easier to accomodate than large round pools, anyways. If your heart is set on a round pool though, I would go no less than 24 feet in diameter, preferably closer to 30.
The dimensions listed above will give you, based on standard above ground pool dimensions, about a 25,000 gallon setup. You would not be limited just to BTR in that setup though - you could keep WTR, zebra sharks, a variety of larger benthics like bamboos, rays, large fish, etc.
I'm not of the school of thought of buying "beginner" animals before getting into "advanced" stuff. That just leaves people with animals that they don't want. If you want to jump into ORV sharks, I say go for it. Just know that it's going to take up a lot of space, a lot of time, and a lot of money.
Just so this doesn't get too long - I will add another post with more thoughts