Here we go, steps, in order, to get an invulnerable world.
1. Make a linkbook to 0,0 in overworld or other central location.
2. Make a small warded stone room to start in. Build it around you. Fill it with sand around you. Once it's just the two blocks you are standing in, drop a falling block (sand or gravel) and do suffocation damage to everything in the block you are. This means even with cheated in ultimate cheat armor, they will take damage and die. You are now alone. Dig out the sand and get started.
3. Take your notebook and make an age, any age, just get it stable.
4. Make a linkbook to the square you are standing in now.
5. Make a few spare linkbooks, do not activate them.
6. Enter the age, if not stable, make new age. Assuming stable move to step 6.
7. Place linkbook back to your warded chamber. Use unlinked linkbook you made here so you can return to this spot. Use linkbook to warded chamber.
8. In warded chamber pick up the worldbook. If there is a nether portal in the warded chamber, somebody broke in. There is a small chance that somebody has used XENO to break in through the wall using the cloak. This is the ONLY moment of vunrability. Place lava, fly above it. Link back to your home world. You will never enter this box again. The linkbook to your homeworld will fall into lava and die almost instantly.
9. Leave the link to the box of death (it's got lava and no exit) sitting in your world in plain sight, if anybody did break in, they might try to escape using it.
10. When you exit, use the linkbook to spawn. Bring a linkbook to your homeworld. Do not use the linkbook unless you are flying above lava.
Your home is now safe.
If PVP exists you will need to make a warded stone box around where your linkbook was made each time you leave, and keep a chest with a replacement linkbook to a new location in the world inside a chest that is inside a very small (ONLY the chest) warded stone block. Each linkbook in a safebox should be to a new location. If you are killed, the warded box they land in where you made the linkbook should have lava placed inside of it. When they come for you, they will simply burn.
