Nah, it will just become "When is 1.3.5"
Yep.
Checked to see if your antivirus is blocking Terraria from accessing/writing to your My Documents folder? This used to be isolated to a few AVs (started with BitDefender), but is now even something WinDef can and does do. Just need to make sure Terraria is an allowed program.
There are established beta testing avenues for both iOS and Android - that is not a worry.
No. It will be an update to your app. Your existing saves should/will transfer over as a part of the process. The system does keep copies of the old 1.2 era saves as well, just in case.
Because that is utter, sheer chaos for a team this size and we do not want a ton of things leaking.
Yes. You *must* have a copy of the paid version of the app for beta to work.