0. In this post I was talking about the retail cartridge.
1. Yes you can use Gateway's Launcher 1.0 and a Backup to update to 4.5.
2. No need to update.
3. It works the same as 4.2, only difference: you are on FW 4.5 now^^ What messes with the exploit is, when you play a Nintendo DS game/rom.
4...