Hello nightperson,
Yes hydroponic lettuce is a lucrative crop. How lucrative? Well that depends on how lucrative you can make it. There are many valuables that will affect your success or failure. But first I couldn't tell much from that website, but it sounds like they just try to sell people systems to go into business with. I wouldn't base any decision on a company that sells systems, they just want to sell their products.

There are many ways to build a hydroponic system to grow your crops in. But if you don't have experience with growing your crop hydroponically, that's a very important aspect to do first (before anything). A single pest infestation, or root disease can ruin your entire crop (and income). So get to know your crop first. Once you know your crop and how to grow it year round (if that's your goal), then that's the time to begin thinking about building a business from it.

But again how lucrative mostly depends on how well you know your crop, as well as your crop quality. Also how well you know how to control pest and disease, know how to control climate, take advantage of the space you have, weather you use natural (sun), or artificial lighting. Not to mention how good you are at controlling expenses like nutrients, water, electricity, packaging material's, gas for traveling to the markets and picking up supplies etc..

But lettuce is one of the most lucrative hydroponic crops. Mostly because they are fast growing (for quick turnover), need relatively low light levels (compared to other crops), and are small so you can pack a lot of plants into a small area (especially stacked vertically). But prices depends the market (supply vs demand) in your area. Your profit depends on your cost to grow vs selling price. Your income depends on your profit per (package, plant, pound etc.) and quantity sold. If there are a dozen other suppliers of lettuce, supplies will be high, and prices/profits low. Then you may want to try another crop with the demand, but less competition.

Here are a few links:
Introduction to Hydroponics and CEA (University of Arizona Controlled Environment Agriculture Center) Scroll down, Each chapter is in pdf so you can print them out. In all the 15 chapters total about 140 pages (printed on both sides about 70 pages).

Small Business Development Centers
Small Business Development Centers (by state) Contact your local Small Business Development Center in your state for a local office in your area. They can provides free counseling in small business start-ups, including creating a business plan.

SCORE
SCORE also provides free counseling with all aspects of small business start-ups, including help creating a business plan.

For selling produce you'll want to be aware of your local health department laws, as well as USDA. I still need to contact the USDA, but our local heath department has told me I don't need a permit or license from the health department to sell produce in whole form. But as soon as you cut into it, it's considered a processed food. And processed foods are regulated, and then I would need a permit to sell it legally.

Also you will want to contact your local Development Services department for zoning laws. In our city, my house is zoned for residential, and not commercial or agricultural. So technically I cant have a commercial greenhouse on our property. But because the green house is not going to be over 200 sq feet (a larger greenhouse would require a permit), and as long as the greenhouse is 10 feet from the property line (to be on the safe side) the greenhouse itself is legal. But as for selling the produce, as long as I'm not going to be selling it from the house, but rather selling it at a farmers market as well as to local retail stores I shouldn't have a problem. Basically I would only have a problem if a neighbor complained about me running a commercial agricultural business on residential property. But as long as I tell everybody the greenhouse is for my private use, I shouldn't have a problem.

I forgot to mention organic produce certification is not simple, and from what I understand can take years to become certified organic. They do fine and prosecute sellers fraudulently claiming organic certification (when they find them). So that's just something to be aware of if growing organic is your goal. Every state and county has their own regulations regarding organic certification. Personally I'm not interested in organic certification, but here are a few links that might help.

National Organic Program (NOP), Organic Certification
National Organic Program
Organic Agriculture: Organic Certification