There are various threads in this board discussing developing for Maemo5.
Just check the developing section

1:
Basically, you need maemo 5 sdk.
If your app only use Qt API, then a simple qmake && make will built it for maemo.

2:
You can build your app in deb, and simply install it on the device
If you'll like to upload the EXTRA repository, you'll need to have a garage account, an approved garage project (wont be hard to start) and you'll be able to upload.
Again: read the manual! there are plenty of resources in this forum and the maemo wiki, If you cant find an answer, you are welcome to ask.

3:
Testing the app in the device shouldnt be hard, you dont even have to build a package or upload anything.
I think esbox can make it even easier.
Bear in mind that you can actually test the application in the SDK without the device.

As a personal suggestion: Although It's possible to develop for maemo5 in Windows, It's better to switch completely to Linux (Ubuntu or Debian). Trust me, the more you use Linux, the better you'll understand maemo.

Goodluck