IOS – ny way to remotly access ios device from another ios device

That totally depends on the apps you want to do.

Do they need GPS localization? A microphone? Front or back cameras? Hi-res camera?

Besides, you can't test an iPad app on the iPhone, so you'll need an iPad no matter what.

Edit: According to the comment, an iPod Touch would be enough for you.

Your question can be rewritten in short form:

1. iTunes: How to move your music to a new computer
2. Where are my iOS backups stored? - expand the section About Syncing and Backups and you'll see

iTunes places the backup files in the following places:

• Mac: ~/Library/Application Support/MobileSync/Backup/
• Windows XP: \Documents and Settings(username)\Application Data\Apple Computer\MobileSync\Backup\
• Windows Vista and Windows 7: \Users(username)\AppData\Roaming\Apple Computer\MobileSync\Backup\

I linked to the official articles since things do change and cutting and pasting the steps today might not be right if things change in a month or two. Don't worry - the article about music moves everything except the iOS device backups. If your device is working, there's no need to move backups unless you want to keep older ones or save time the first time you sync with the new iTunes.