I am going to qualify this and say I don't have a ton of experience with tillers as I am also making my first crossbow! But I have made gun stocks. So here is my advice. You'll probably find a 2" wide stock is a bit large unless you are unusually gifted in body mass. I would pick up a 3/4" board and laminate it so you'll be starting at 1 1/2" inches. This is where most rifle stocks start their life at. When looking for a board, check all the angles for warping, try to get the straightest piece. Most likely it will have to be the best of the lot rather than perfect. Highly figured wood is most often the prettiest but weakest wood. I would look for something that has grain lines echoing your tiller design or at least putting strait grain where the pressure of shooting will be the greatest. I would get a single long board cut it in half and mirror the wood grain so the natural pressures of the wood work against each other. It'll help prevent the wood from further warping once the tiller is done. It will also help you square up any current warping in the wood (assuming you don't have a jointer that will square up the wood for you). You can do all the cutting out work first, the key is to have some kind of registration system so it all fits back together easily when you go to glue it up. Glue up is simple if you pieces fit together well, painful if they do not. You won't need dowels with a good wood glue like Titebond 2 or 3, just well mated surfaces.
To do the job you would need a saw, sharp chisel, drill, clamps, and something to hold your work on. A plane and square would really help you to square the bits that need to be square. I find that is the toughest part of using hand tools getting thing square. A good rasp and cabinet scrapers are wonderful for shaping the wood where it needs to be shaped. I use a saw rasp (without the dorky handle from the link) cheap, very effective, and doesn't clog up much. Forstner bits are great for making pretty round holes. Drill presses, bandsaws, and plunge routers are all great tools that allow you destroy your work much more quickly than you can with standard hand tools. A good sturdy vice is a gift from the Gods. The one I use most is an angled drill press vice anchored to piece of plywood and then clamped to my work bench. Its very versatile and allows me to quickly pivot my work piece, rather than try to contort around it. But saying all this, most medieval style tillers are pretty simple from a design stand point and only need a minimum number of tools to get done. Other tools will just get it done quicker.