When developing apps for iPhone and iPad?

Do you recommend me having at least iPod touch? Or both iPod touch and iPad? I have neither, but I'm

If I go to Apple Store and ask they will of course say "yes you need both iPod touch and iPad"

It kind of depends on which device your apps are geared towards. Just because something will run on both doesn't necessarily mean that it works well on it. Have you ever tried to play Draw Something on an iPhone or iPod touch? It's awful… That app was absolutely made for a larger screen even though it will run on anything that runs iOS.

Ultimately you can't be certain the APP will work B4 installing it on the target device… So build a list of friends that are willing to test the APP for you

If you are going to be developing apps that are optimised for iPad then it will be very beneficial to you to have the iPad, otherwise an iPod Touch or iPhone will be fine.

You actually don't need a device (except of course a Mac computer); the apple dev kit comes with an iOS simulator. Which means you can test your app on a virtual iPad / iPod / iPhone.
What you do need is money to buy / license the dev kit and knowledge of Objective C.