My good JJon, we meet again
Let me tell you that if you are mining, unless A: you can tell for sure it is someones place, then you're free to mine, use a wooden pick and right-click with it to see if anyone has place that block, now if it is a mine-out room and there is lava there, it is fine to take it, lava is ussually not used in mines because it is too hazardous to be used for mining purposes, it is more likely to be ued above-ground as traps or moats.
If it is in the "Mining World" Go straight at it, you are not supposed to build in there, so it is fine
As for your second question, you may gladly join the town i am apart of, all you need to do is ask or type /t list what that will do is show you available towns (Towns that are alive, you can see the information of that town by typing /town [town name no brackets
]) here is an example /town Empire that will show you some information about the town, such as the towns mayor/owner/lord depends on their title.... anyway, it will show you who town assistants are, aswell as town residents, how many there are and some other information, i am in the town Empire, ask EmporerMyrf to add you to the town next time you/him are online, if you like and if you join Empire, you can live with me at my outpost.