Of course, denser woods give a lot thinner bows. I think I mentioned it, but I've got another norwegian yew longbow which is a lot smaller and still 40 punds heavier than this one. I once handeled a Stratton 120# flightbow, which looked like a 60# bow. It was really heavy in weight though. Yew usually gives a larger bow for a given weight than other woods. Ipe for example...
A nice experiment would be to make two replicas of the smalles MR-bow, one from dense yew and one from less dense yew. If nothing else, it would give an interesting new set of data for the interpretation of the MR draw weights. As it is now, we only seem to have the upper limit setteled to be from 200 to 120#. - so there's really no good evidence to back up any statement on what the lower range of draw weights was like.
The more you twist a string, the more stress you put on each fiber, which results in more elastisity with the stronger stuff and more risk with e.g. linnen. So I usually twist them no more than necessary for them to hold together while also making sure the cross section stays reasonably round. This is a 3x5 ply ff+ string. That one is overly safe
The less you twist the less strands you can get away with, so with flightbows I twist them even less.
And just as a general comment: When it comes to constructive comments and spots on the tiller...
...a picture is really not enough to give detailed advice. To do that you need an overview of things like local density of the wood, knots, amount of sapwood/heartwood, the shape of the cross section, the shape of the natural growth and most basicly - the width of each section of the bow. What pictures are good for are considering the gereral shape of the tiller compared to the width-profile of the bow, and of course for considering symmetry.