So what is the point to have high stem then ? is it only visual thing or have it something to do with big lakes and waves ? Can I still use lover stem even if i have molds for 18 inch stem? Is it possible to attach first strip bit lower and by doing so, getting lower stem?
Yes, to all of that. Taller stems will shield you from bigger waves for sure. And when you're stripping, you can add wood all the way to the design height. Later, when the hull is flipped over and you're ready to trim the sheer line, you could trim off as much or as little as you like, based on your NEEDS and your DESIRES. I will admit there is a pleasing look to a gently upswept bow, but I personally don't care for the super high stems that are seen on some vintage and classic hulls.
But a quick (or maybe not) note about bigger waves and taller stems. A canoe with some forward flare will keep you drier in large waves than a taller stem will. The flare will force waves away from the hull. Also, a hull with a bit more rocker will ride up larger waves better than a straight keeled hull, which would slice through waves (great for tracking, but not for staying dry). And remember, staying dry is not just a comfort issue, it's also a safety issue. Take on enough water in big waves and you no longer have the buoyancy you once had when dry and empty.
There's much to consider in a canoe hull design, which is why most guys (and gals) prefer to use a proven design. A few brave souls (Alan, Jim, sometimes me) branch out and do custom designs based upon previous experience.
Ultimately, you need to decide which characteristics are most important to YOU. On water performance, safety, aesthetics, weight are of different importance to each of us. Ask the other guys here that have built that same design, and see how well their impressions align with your desires. This could lead into many, much more in depth discussions, so I'll stop here...