Car engines... converting a car engine for aircraft use isn't a simple thing. There are several successful conversions, most notably older Volkswagen and Subaru engines, but it's not just a matter of going down to the salvage yard, picking it up, and bolting it on. A relatively light engine like a VW Beetle engine might be suitable for a FIN; a heavy Chevy V8 would not.
How much "canvas"... none at all. Canvas isn't used, and anyway as I told you above, you won't be able to make your own sails without years of experience and an expensive industrial sewing machine.
I see that you want to build a glider with an auto engine, and control an artificial center of gravity using the dashboard/control panel/throttle.
I appreciate you eagerness to get into the air - most of us here are just as interested in flying as we are designing and building.
Your questions clearly indicate that you are not familiar with the basics of aircraft design, construction and operation. Why not take the time to go to some locations where people are successfully operating the kind of flying machines that you are interested in, get a basic education about them, go flying in some, perhaps even get qualified to fly them yourself, then consider your plans to design and build? That approach will be safer, and less costly in the long run.
People here are willing to share their knowledge and experience, but a knowledge of aircraft terminology as well as a basic level of understanding is necessary to even ask appropriate questions and to understand the answers. So stick around, learn, and share your design work with us when you get to that stage.
GliderBoy I'm sorry to steer you in a direction that may seem less interesting or technical, but please understand that there are several experienced people here who are trying to steer you in a safe, sane, and responsible direction already.... and I'm simply adding my voice to theirs. I'm definitely not an expert in the type of flying boats you are asking about, but I'm pretty certain that any experts in that area would agree with the opinions and advice below.
The type of aircraft you are asking about more or less already exists. If you want to create a new twist on it, or eventually build one yourself, the people on this forum will GLADLY help you and offer valuable assistance, discussion, etc. There is an unbelieveably huge amount of brains and experience in this forum, from every corner of the world. They've already started to help, you just need to let it happen.
One of the ways that the people here will help you is by keeping you focused on things that are realistic and safe. Please understand how important that is.
Just like someone who wants an exotic car, or an exotic job, you have to start with a normal one even if it's just for a short time. This is especially true in flying/airplanes/aviation. All we're telling you here is that you should get a few flights in something similar to what you wre asking about.
Find a REPUTABLE ultralight organization in your area. The US Ultralight Association has local chapters and can offer referrals to local ultralight organizations that will keep you safe, and provide you with good instruction. You really need to get started on the right foot, and not get involved with known scammers, or posers, or unsafe operators. Flying is not as much fun when you're dead.
Plunk down a little bit of your money, and take one or two introductory lessons. If you can find a place where they have "weight shift" controlled ultralights, then make sure you do that as well as trying the "traditional" aero controlled method as well. Spend time walking around the ultralight aircraft of all shapes and sizes. Pay attention to how they're built, what holds them together, and how things work. Ask a million questions, get two million answers, and start figuring out who knows what they're talking about and who the Bozos are. You don't know this yet, but your life depends on it.
For right now, you should forget about sewing your own sails, doing your own engineering, or re-designing an entire flying machine. All those things are of course what this forum is about, but you're not ready to go down that path just yet. Right now you need to start flying and start learning about the technology/mechanics/physics of the type of aircraft you are flying. Since you know you are eventually looking to build and operate a flex-wing weight shift flying boat, then start to study those machines. Look at all the youtube videos with these types of aircraft. Start reading the ultralight magazines and websites.
One of the most important things you can do in the near-term is plan on going to the Sun 'n Fun show in Lakeland Florida this Spring. They have by far the largest gathering of people and equipment for that type of flying in the world. It may be a long drive to get there and back, but you will see and learn more in one week than you could in a year of web surfing.
Thank you everyone for your advice, I’ll try and read up on all those subjects, and maybe I’ll come some another time well-educated in the art of airplane design. We will postpone are project, so thank you for helping and for the kind advice.