1. My old (2-3y) paper wallets are generated with bitaddress.org, is it still considered safe? I use it on a Air-Gapped PC with ubuntu live usb stick.
Probably, if you downloaded it from a trusted source or you verified it yourself. I'm not aware of any vulnerability affecting it as of now.
2. I'm going to move funds from paperwallets (pre segwith), so I have also Bitcoin cash. Going to move it to other paper wallets. How should I move it? I guess I also need a paperwallet for my Bitcoin Cash?
You can actually just use the same address for both Bitcoin and Bitcoin Cash, they are generated the same way and they do have replay protection. If you want to move it, I would suggest for you to decrypt it using bitaddress and import it into Electrum. You might want to do it in an airgapped condition if you want the maximum security
3. A reserve android phone with Mycelium app installed is very temping, I can scan the private QR code and scan the receive address of the new wallet and move it?
What do you mean? The Mycelium cold storage function should be fairly safe, and you can use it without problem though it is not the most secure as compared to an airgapped Electrum.