Not getting much help here? Self bow boys must be sleeping. I will give it a go...
Sureform and rasps will work fine. I personally like my nicholson 49 and my shinto the best. I use a drawknife only to remove bark and sapwood, remove large amounts of wood to rough bow dimensions (if I don't use a bandsaw), and to chase a ring on osage. I would recommend a cabinet scraper. I use to tiller once the bow is bending a bit.
Dimensions - either design would be ok for the ash. I would get as much width out of it as you can. If I was making it, I would probably keep the width parallel out to about midlimb and then taper to tip. (But pyramid would be fine too). If I remember, you said your draw length was around 27". I would make it at least 64" ntn and you should be able to get 50# out of that stave.
Heat Videos - Yes, a lot of good videos on Youtube on using heat on stave. John Scifres has a pretty good one -
Or you can just google it and get lots of options. I would personally use a heat gun, caul and clamps as shown in the video.
The caul will allow you to add a little reflex and straighten at the same time.
Peculiarities of ash: Its not as good as osage. :D It will make a bow though. Go slow, be patient, it will take set and lots of it if you get carried away during tillering. Don't pull more than your desired final weight, don't pull beyond the point you see something that needs attention. Heat treating the belly will make it a bit "snappier".
Good luck.