"I need the screen to be big. I want to be able to write easily with a stylus on the screen (with no pause and delay)."
My immediate reaction is to say forget the iPad idea - it's an expensive option,and there may be better solutions. The screen may not be large enough for your purpose.
You could buy a touch-screen laptop and use a stylus to write in an application called 'Windows Journal. The software will convert your handwriting to text, which you can then copy and paste into another location - this forum for instance - or save as a journal document.
Alternatively, you might consider voice recognition software that would convert your spoken words to text.
I might be more help if you can tell me more specifically what you mainly want to use your computer for.