Well, bad news for you--a red dot's not going to solve your astigmatism. It could actually make it worse. Astigmatism gives the dot a big, uneven corona. In severe cases, you can wind up seeing a figure-8 instead of a dot.

A low, fixed-power scope might be right up your alley. Going with a fixed as opposed to a variable magnification gives you a lot more durability, important on a gun with this kind of recoil.

I'd give up on an IWB for the 460--there's a reason nobody makes one for X-frames. Instead, there are a lot of budget-friendly CCW-able pistols and revolvers that would do the job much better than the 460 ever could (even loaded with .45 Colt). Flip around the classifieds here. There are all manner of J-frames and small autos that'll work just fine. No sense spending $100 on a holster for the 460, when you can find a good J-frame for under $400.