Every bow you make or attempt to make is a learning opportunity, and on top of that you can also stand on the shoulder of giants.
My advice for this bow: narrow the tips to 1 cm wide, and make the mid-limb section bend more. Don't worry too much about the poundage just now, focus on the tiller. It is quite a long bow, and you can easily add a few pounds later on by making the bow 5 cm or so shorter (while also maybe reducing a bit the draw length).
If you're short of decent staves, there are many options described by Tim Baker in the Traditional Bowyer's Bible Vol1 (and 4):
1. Go to a hardware lumber store, find the most straight grained board you can find, make a pyramid board bow, 65 to 70" or so, 2" wide, and the tiller is nearly automatically correct if you keep the thickness equal across the board. Aim for 12-13 mm thickness (1/2") and you'll have a 40# bow or heavier from about any wood. I've made decent enough bows even from pine lumber, but if you can find some oak, hickory, ash or so you're ready to go.
2. Look for ash broom sticks, as straight grained as possible, and make a 72" longbow. You can also splice together two pieces of hickory or ash from pick or ax handles, all you need is a steady hand and a good hand saw for a Z-splice.
3. I've made loads of (often smaller) bows from 1" wide branches of plum, hawthorn, elm, ... heck, even from a rose (yes, those with the flowers). You can scavenge road-side hedges and you'll find tons of useful staves that will give you 30-40# bows at 26". Harvest, debark with a pocket knife, whittle out the rough bow dimensions, let it dry for a few weeks (weigh the moisture loss regularly) and use these to learn to tiller. Such bows can be made in the course of a few hours, even by beginners.
So no reason to wait for summer, all you need is a hand saw to harvest branches here and there, a rasp to rough out the bow and tiller roughly, a drawing knife to scrape (or a regular large knife), and a grindstone to sharpen the knives ;-). You don't need days to make a bow: every day half an hour so and you'll make steep progress soon.
good luck, and keep these bows coming
J