Sorry to hear about the Ipe bow. Looks like it might have been too dry? Hard to tell though.
Onto the interesting bit...
That knot may or may not be an issue. It has got a ring of black gunk around it which might be cause for concern, but it's not in a dangerous place within the stave and even though it's poking through the back you SHOULD be ok. However, you'll need to wait a bit to see how it looks as the bow starts to flex. Or, I suppose, if you're super worried about it, give it a dig and see if it just drops out once you start removing the black stuff. If it stays put and really won't budge, superglue. If it falls out, do what I said in the PM and stuff the hole with a good solid mix of epoxy and yew sawdust, or even a Dutch Plug - make a long dowel of offcut yew and push it all the way through the hole where the knot was, leaving a bit sticking out each end, then remove the excess.
Everybody you ask who knows their warbows will tell you to always chase a ring with Pacific yew, if you're aiming for something over 100# or so. The sapwood looks a bit too thick from the picture of the end grain, so you'll probably have to reduce it anyway, at which point take your time and get down to a single ring but do it in stages.
74" is just long enough to push a 32" draw with a heavy bow (what weight are you going for?) and it's also the absolute minimum length allowed in the EWBS.
At this point, what I'd be doing is marking a center line, and drawing out your front profile bearing in mind what I mentioned earlier about Pacific yew - go slightly wider than dimensions of Italian yew bows - 40mm should be perfect. You can find fairly rough dimensions in Secrets of The English Warbow, but you're basically after a long middle section staying around 40mm wide, almost right up to mid-limb. At that point you should taper to 22mm thick tips. Cut that shape out and use it as you're tillering, but bear in mind the final tip width should be around 12mm. The wider you can leave the tips to start with the better, in case it wants to twist as you're teaching it to bend.
Once you've got your front profile roughed out, reduce the sapwood. You'll have a better idea of the ratios once the front profile is roughed out, so you won't need to spend hours chasing an entire stave - just the bit you need! You then need to decide on a belly profile - avoid the D shape of Victorian bows and some of the Mary Rose bows, and go much squarer - a bit like a rectangle that has no edges.
