There are many changes coming to the TNTable SMP server with Minecraft 1.18. Check this post out for the details and what it means for you.
Minecraft 1.17 is the first part of the Caves and Cliffs update. The server world will not be resetting until the second part is released.
Using Waterfall Velocity, a Minecraft server proxy, you only need one address to be able to connect to multiple servers.