First off, you dont need sinew and i dont recommend it for your first few bows. hickory is as bullet proof as you get and you have plenty of length and width for the bow you want. What is your drawlength? I would make a pyramid style bow if you have enough thickness for a handle. If not i would do a simple bend through the handle D-bow that doesn't narrow in the handle. Keep the tips at 3\4" for now, you can narrow those at the end of the process but it is nice to have some width to make adjustments with as you go. I really recommend that you do some research so that you have a fairly clear idea of how you are going to lay the bow out before you remove any wood. the best thing you can do is find an experienced bowyer in your area have them give you some pointers. What area do you live in? It's likely that someone on this site is nearby. As for your thickness, once you have your design laid out you should start removing wood from the belly evenly and carefully until the bow is just starting to bend when you press a tip into the floor. From there you keep carefully removing wood from the belly and checking the bend frequently against the floor. This is called floor tillering.