I'm not a small businessman, but I am a fisherman, and I'm not sure I see how the numbers here add up to a profitable business.
If you are talking about 30 and 50 yard spools of fluoro, can I assume you are talking about selling this as fly fishing tippet? If so, the "big name" players (to the degree "names" exist in a niche market like fly fishing) do sell for around $15 per 30 yd spool (a few for considerably more). But they usually have a range of products to go with their tippet (like leaders and fly lines) a recognized brand, a reputation for customer service, and a marketing budget that gets them out in front of a lot of fly fishermen.
At $18 for 50 yards, you really aren't undercutting these companies on price by a significant amount, so you will have to sell based on the superiority of the product. If this Japanese tippet is really significantly better than what established companies produce, you're going to have to quantify this and get it out in front of fly fishermen. How will potential customers know your product is better? Why will they believe you? My guess is that this requires attendance at trade shows, placement in magazines and use by pros, guides, etc. That all takes time and money. And if the product really is superior, unless you have an exclusive, other companies can simply buy the same product and market it themselves.
It also looks to me like there's a lot of competition. I buy fluorocarbon tippet, but I usually buy when it is on sale, so I get a name brand for under $10 per spool. And unlike mono tippet, fluorocarbon doesn't degrade with age, so I don't have to buy every season, and I can wait until I see a really good deal. There's a lot of choices for fluoro tippet in 50 yard sizes for under $10 on Amazon from companies I haven't heard of. As an unknown product, you'll probably be competing with them as much as with the big boys.
To turn a profit, you're going to have to sell many thousands of spools of this fluoro. And doing all that by direct sale is going to be tough. If you get it into Cabela's or fly shops or Amazon, you might sell more, but your margins are going to be a lot lower.
I'm trying to picture myself sending $54 for three spools of tippet to your company (plus postage?), and it is a little difficult. Tippet is a product I like to buy from a local fly shop to help keep them in business. If I go mail order, I could pay $45 for the product I usually buy in 30 yd spools, maybe $30 on sale, or about $15 for a generic product. Both of those options seem more likely.
All that said, I think being in the tackle business might be really interesting, particularly if you're more than just a silent partner. If the product really is superior and you're willing to invest in things like having a booth at the fishing tackle shows, it could be fun, especially if you can afford to lose your $5,000 investment.
I'd have a look at the proposed business plan and look to see how that $70,000 would create a market for the product. I think you'd have to sell a lot of tippet to turn a profit on a $70,000 investment.
Good luck!