Do we have to support 3.5 inch screens?

YES, you MUST support the 3.5" screen. The iPhone 4s is still amongst the supported devices

and will continue to be when iOS 9 ships this fall, Apple has said so very clearly. Also, unless

you're writing a universal app, your iPhone app MUST run in 3.5" 1x/2x compatibilty mode on

the iPad family.

I read somewhere that developers are now allowed to ship apps that require 64 bit hardware (I didn't see the WWDC video where this was announced, I read it on some blog so...it could be misinformation, though I have no reason to believe it is).

In theory, Apple could release a 3.5 inch iPhone in the future with 64 bit support, so relying on that could cause problems in the future (and your app would also have to be universal...if it's iPhone-only it may still run on the iPad in compatibility mode...though I'd think by now they would change that to have the iPad scale up the iPhone 6 Plus layout instead.....I imagine that would look better than using the 3.5 inch).

Handling the old 3.5 inch iPhone can be a pain for some designs...because it's smaller and the proportion isn't the same as the other iPhones so certain "design things" cannot be solved with math.

I'm actually with you on this one. i think it's really a terrible idea to ever hard code software. It never ends up working out in the long run. Thankfully I've been able to deal with the 4s issues a little here and there but it still causes limitations. I'm sure there will be a feature in Xcode 7 or 8 in the future that will make it easier to take advantage of screen space.

Okay. So in the past, it used to be possible to use a story board dedicated to iPads. Do you know if you can still do that? Right now, I've managed to get everything pretty much up and running on the iPhone, but I do eventually down the line want to make this a Universal application. Again, I want to be able to take full advantage of screen space and the iPhones limit that severely.

Yeah hard-coding *****. I don't use autolayout, but I position subviews relative to each other and the screen. For certain layouts the 'shorter size' of 3.5 inch iPhones doesn't get in the way but sometimes it does.

If you start designing from the smallest screen size and work your way up...you should be alright, but then you won't be taking advantage of the larger screen sizes...you're just blowing everything up. I have a class that returns a screen type. When the 3.5 inch iPhone's aspect ratio gets in my way, I typically do something like

-(void)viewDidLayoutSubviews
{
  [super viewDidLayoutSubviews];

  if (self.screenType == IPhone4ScreenType)
  {
    //alternative layout or constraints for different aspect ratio.
  }
else
{
     //Layout or constraints for everyone else.
 }

}

While using math for layout is useful, I wish Apple would have innovated a bit more on this. It would be nice if Interface Builder provided a solution geared more toward handling alternative layouts...instead of just giving us a square box to tinker with. There's a pretty decent 'trial and error' process involved with doing layout in IB.

There IS a solution available - it is called size classes.

Size classes don't help with 3.5 inch screens.

They do, if you begin your design on 3.5" devices.