I’ve misunderstood something - I need to create a portal at Therka market as well, or I can hook into one that somebody else has already built?
You’ll need two of your own, unless someone is willing to give you a portal token from their own portal - a portal can only have a single destination.
Do I need to own land to place a portal?
Anything outside of a beacon claim will degenerate after eight or so hours unattended, so yes, you should beacon all your builds if you want to keep them safe. That includes your portals.
You can hook into somebody else’s as long as they give you a portal marker from there portal or vice versa
You’ll need two portals to connect to each other. You need both portals to be inside a beacon, but not necessarily your own.
The portal you’re introducing the portal token in, will be the only portal that needs powering up. You can create a portal in other platyers beacon as long as they grant you beacon permission.
For instance, the temple portals, are inside plots shared by the donors.