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Establish communication between Universal app and Standalone app developed with Unity3d

I have a UWP app and Unity3d app build for Windows. I have a requirement of establishing communication between UWP app and Unity3d app.Both apps will run on same computer.
Development of Unity3d app and Universal app(Windows 10 native app) both are done in C# language.
Communication should involve:
Launching and closing Unity3d app from UWP app.
Send data from UWP app to Unity3d app.
Receive data from Unity3d app to Windows native app.
I had searched for resources for this but unable to find any. Could someone please share possible ways to achieve the above and resources/examples for those.
Thanks :)

i did this via an Appservice: https://msdn.microsoft.com/en-us/windows/uwp/launch-resume/how-to-create-and-consume-an-app-service in your normal xaml app host the app service and let unity consume data from it.
And via protocol activation the apps can start eachother.

Push Notification Service for WPF based desktop app?

I need help to choose a Push Notification Service for my WPF desktop based app. I was checking on Google's Firebase, Windows Push Notification Services (WNS) etc but they all speak in context of App based environment i.e. iOS, Android or WP. Further more they have documented references for Web Apps using JavaScript.
Now i am stuck to find one which is compatible for my desktop based WPF + C# App.
Can anyone help me please?

It wouldn't work unless you convert your app (No matter if it's WPF/MFC/other desktop tech) to UWP/Store app.
Fine details are listed here:
https://msdn.microsoft.com/en-us/library/windows/desktop/mt695951(v=vs.85).aspx
Reason: WNS Push notification API doesn't support DualApiPartition attribute:
https://learn.microsoft.com/en-us/uwp/api/windows.networking.pushnotifications.pushnotificationchannelmanager

As mentioned in the comments by Wolfgang you can use Azure Notification Hubs. If you install the NuGet package Microsoft.Azure.NotificationHubs you can then use that to subscribe to notifications. It requires a minimum of .Net 4.5, so long as your WPF application is targeting that or higher you should be fine.

How to connect an xbox360 controller to a desktop app (C#, Windows 10)

I am looking to write a simple app which accepts input from an Xbox 360 controller. I am developing in C# and my current dev environment is a windows 10 machine.
I've attempted to install XNA studio 4.0, and got a system notification saying that it isn't supported. When I clicked on the notification for more info, I was redirected to a webpage which started a Windows Live Gaming installer download.
This seems to rule out XInput.
I thought my alternative was to use the Windows.Gaming.Input namespace, but it seems to be limited to metro apps.
I don't know what are my other alternatives.
What is the correct library for me to be using, and where do I download it from?

XINPUT will read the Xbox One controller with the drivers currently on Windows Update, but you will be unable to access the 'impulse trigger motors' using that API. For C# usage, look at SharpDX or SlimDX.
You can use Windows Runtime APIs from desktop apps including Windows.Gaming.Input. They key is you have to initialize WinRT with Windows::Foundation::Initialize.
See DirectX Tool Kit: Now with GamePads. If you were writing in C++, I'd also recommend looking at the DirectX Tool Kit GamePad class.

How can develop Windows C# App using BLE

I'm trying to develop a windows app that communicate with bluetooth device.
Now I have one bluetooth-usb dongle for my windows desktop and bluetooth BLE device.
I want to develop the app using C# and Visual Studio in Windows 10.
But I can't find official documents and APIs at all. There's no C# API about BLE in windows? If it is, How can I develop a C# App using BLE?

The Microsoft Bluetooth team did a Build talk which includes BLE sample apps for GATT Server, Beacons, and Pairing. You can find the GitHub repo here.
A Build talk about Beacons and reading from a GATT Server can be found here.

There is a BLE example included in the Universal Windows sample programs provided by Microsoft. It is called BluetoothGattHeartRate.
Not that this is the end all, but it does get you going. It would be nice, given the whole IOT push if they had a Windows Bluetooth developer example that made configuring, and all the features really simple...

How do I real time communicate a Universal Windows App with a older .Net 4.5 app in the same solution. IPC?

I have been struggling with this for over a month, but am slowly learning. Here is what I have:
C# Solution With 3 Projects
-Universal Windows Platform App (Cortana Voice Support)
::Above just shows a floating PNG image and is Cortana enabled
-Universal Windows Service (Cortana Background Service)
::Needed for the Cortana Support
-.Net 4.5 C# App with HTML DOM Automation
::Automates locating elements and clicking of a website
I can't re-code my .Net app's functionality in my Universal app because some of the libraries it uses won't install. (GhostDriver, PhantomJS, and a HotKey Library provided via NuGet. Installing on the Universal Platform fails on all 3 libraries).
What is needed:
-Master Universal Windows App or Service sends signal to .Net App
-.Net App receives signal and calls method/function providing my functionality.
I've never tried calling methods in other apps within the same solution and was wondering if there was a few-code workaround. What I need I think is a method of inter process communication or events, but can't find any examples of a UWP. Most are .Net communicating with other older non universal apps.
Thank you so much!

If I understand correctly, you were developing a app which will can automate the DOM operation through Cortana.
Do you need to submit this app to App Store?
If no, as Scott said, you can use WCF to communicate between UWP process and .NET 4.5 desktop app process.
If yes, as Andrew pointed out, you need an intermediate remote server hosting the service.