Not necessarily. As always, the answer is "it depends".
If you're looking to get into high-end, room-scale VR with hand-tracked controllers and high-fidelity graphics, then yes. You need a Windows 10 PC with as much RAM, CPU, and GPU as you can muster. Plan on spending at least USD 2000 on a custom-built PC.
If you're looking to get into smartphone-based AR, you can use practically anything to write the code, and there are plenty of tools to be able to build completely cross-platform apps. But you will want a flagship phone, whether that's the latest iPhone or one of the Androids with a powerful CPU and GPU. AR is very CPU intensive. While there have been demonstrations of SLAM on GPUs, all of the implementations I'm aware of are doing it on the CPU.
Where should you start? Well, without hand-tracking of some kind, I don't really consider it VR. Google Cardboard, Google Daydream, Samsung Gear VR, and Oculus Rift without the Touch controllers are all glorified 2D interfaces. They don't provide anything actually new in terms of being able to interact with the application.
Smartphone-based AR apps will probably reach a wider audience sooner than VR. But if Microsoft's approach to headsets and Windows Holographic pays off, I think that is not a perpetual state of affairs. Ideally, this gets down to the size of a pair of sunglasses (which is very nearly the case already). At that point, smartphone-based AR is going to be a quaint novelty.
2000 USD is too high for the cost of a VR PC. I built a PC in fall 2016 that was more powerful than what was required for VR and it cost me around $1200. Additionally there are companies advertising "VR Ready PCs" that come with an Oculus headset for around USD 1,000. See this article: https://arstechnica.com/gaming/2017/01/dont-look-now-but-ocu...
Check out the Samsung Gear VR and Google Daydream if you have a compatible smartphone. If you don't you can use Google Cardboard (I believe even with iOS).
From a development standpoint the main difference between mobile headsets and PC headsets is that mobile VR doesn't track the physical position of your head or hands. However you can still learn a ton and make a lot of cool things with them.
I have a Google Pixel and Google Daydream and am an Android programmer.
If you have these things you can go into Google's Daydream store and download some Daydream apps, free or paid. I have done so and virtually every app has a logo somewhere said made with Unity. Each app seems to be multi-platform - it is made with Unity, and exported to Google Daydream, Oculus, Gear VR etc.
I programmed a basic OpenGLES shape in Android Studio for Daydream, but there was a lot that was lacking. I suspect most people will use Unity, and target the various VR platforms.
So in general, the answer is you need a platform Unity is on. Which in production is MacOS and Windows, although they have a Linux beta from what I understand.
Nope. I just recently did a VR project for school, and we did it all with a Gear VR using Samsung phone's. The interfaces aren't the best, but you can make things fairly portable so you could always move to a PC later if you wanted to.
No! To get started, there are many opportunities for VR dev on smartphones. You can even start working with hand-tracking with the new Samsung Gear/Google Daydream!
However, you do need a PC with a pretty good GPU if you want to get serious about playing with more advanced systems like the Vive and the Rift. (This was a great resource for me when I built my PC! http://www.logicalincrements.com/articles/vrguide)
If you're looking to get into high-end, room-scale VR with hand-tracked controllers and high-fidelity graphics, then yes. You need a Windows 10 PC with as much RAM, CPU, and GPU as you can muster. Plan on spending at least USD 2000 on a custom-built PC.
If you're looking to get into smartphone-based AR, you can use practically anything to write the code, and there are plenty of tools to be able to build completely cross-platform apps. But you will want a flagship phone, whether that's the latest iPhone or one of the Androids with a powerful CPU and GPU. AR is very CPU intensive. While there have been demonstrations of SLAM on GPUs, all of the implementations I'm aware of are doing it on the CPU.
Where should you start? Well, without hand-tracking of some kind, I don't really consider it VR. Google Cardboard, Google Daydream, Samsung Gear VR, and Oculus Rift without the Touch controllers are all glorified 2D interfaces. They don't provide anything actually new in terms of being able to interact with the application.
Smartphone-based AR apps will probably reach a wider audience sooner than VR. But if Microsoft's approach to headsets and Windows Holographic pays off, I think that is not a perpetual state of affairs. Ideally, this gets down to the size of a pair of sunglasses (which is very nearly the case already). At that point, smartphone-based AR is going to be a quaint novelty.