From what I have read, there will be no elevators. It will be an underpass, which would probably mean a gradual ramp under the tracks on both ends. That's a good question about the ADA. I use a walker, which is narrow enough, but a wheelchair is wider. I hope the other Betty is correct that there would be signs telling cyclists to walk their bikes.
That's gonna have to be a hell of an incline to that ramp....there is not that much space between the station and the tracks, unless they do something like start the ramp INSIDE the station and excavate from in there.
Also, given Illinois' precarious finances, I really wonder if we're ever really going to see that second track used, or if this is just going to be another expensive project to line the pockets of some politically-connected contractor.
The work on the second platform is funded by the federal high speed rail grant. Work on the underpass, if/when that takes place, would be paid for by local and/or federal funds. The state's fiscal situation likely will not be a major factor here.
EDIT: Check out page 51 of
this pdf. It shows what the Town of Normal has been looking at in terms of the underpass. The ramps would be aligned roughly north-south to connect with the Constitution Trail. There would be stairs next to the station platforms. And it mentions elevators next to the platforms as well.