Ok, let me start at the bottom. A lot of the YT info is simply outdated - things in this game change occasionally, and what was true half a year ago does not need to be true now. And yes, showing how you can earn a lot of money in a short time in a big ship is misleading - or at least not very useful.
As far as external sites go - EDDB, EDSM and Inara are correct. They may, although, be incomplete or out of date. These sites are automatically fed with data from CMDRs playing the game (on PC, mostly) who are running the automatic update tools in the background. EDTools is mostly correct - most of the data they're using comes from the same database as EDDB (IIRC), other stuff (like the location of overlapping hotspots) is added from the miners on the ED miner's reddit.
Coriolis and EDSy are mostly reliable, they may be off by a few percent here and there - the proböem is that ship stats aren't as easy to come by as market data, and there's a lot of research behind the numbers that are used there.
Back to your original question, though. You want to go mining for LTDs? Any specific reason to choose LTDs? Because these are some of the most difficult to find and mine minerals, while simultaneously among the hardest to sell. Mining Painite is easier and faster. But it's your trail. If you post your location and ship's loadout (the latter preferrably as a link to a Coriolis build), someone will hopefully show up and be able to help you better. For me, it's been months since I last mined LTDs, so my knowledge may well be outdated.
What I remember, though, is that LTDs were only available as core minerals. Meaning you will need a PWA (pulse wave analyzer, which is reportedly broken right now) to find them and a seismic charge launcher (which will need a medium size hardpoint) to crack these rocks open. The smallest ship that I'd use for that would be a Diamondback Explorer (DBX). Laser mining (e.g. for Painite) can be done in a Sidewinder (not that much fun, though) or a Type-6.