1. You can only build a charter stone on a village claim. Without a village claim, it will become and remain inactive (for example, if the claim totem is destroyed or the claim runs out of presence).
I tried to hunt down the visitor and charter stone rule, but I must be looking in the wrong place. Apologies if I got it wrong (I'm sure someone will correct me... they always do.) My understanding is that no, you can't siege from transporting in via charter, as you get the visitor flag. There were several occurrences of exploits and other shenanigans before that was implemented if I'm recalling things correctly, both with just transporting in, and with abusing certain mechanics of spawning in new characters.