Maybe this isn't the best place for this post, I'm not currently running Planeplotter but I suspect I should be.

I host a FR24 receiver, feed it to my home PC running Virtual Radar Server for my own entertainment in my own home. I'd like to do more and this is where I need help.

I'd like to be logging data for more than what seems one day with Virtual Radar Server.

Is there a way to see if a receiver is hearing interrogation modes 1-5 or A or C but not displaying them because they are encrypted / location unknown? How do I log or track aircraft that do not show up on fr24 website or my internal Virtual Radar Server live tracking or historical screens but I know they are there and presumably broadcasting some interrogation mode from their transponder? After all, there is more than ADS-B on 1090MHz right?

How can I make multilateration available in my poorly covered home area?
Either publicly on fr24.com, for the Planeplotter community only, for my own internal use only, or all of these?

If I am able to place another ADS-B receiver at another location, will that help me with establishing mlat?

How far apart do they need to be, a few miles, dozens of miles, different counties?

I know that's a lot and I've read many other posts, I have a vague general idea of how some of this works but I don't know of a good summary that explains all of this.

Oh yes, instead of a free receiver from fr24 or the other big website, should I just buy my own receiver that is an all in one box that can receive and log everything? Is there such a thing and what is it called?

Thanks!