You are right in thinking the LFG is a very unintuitive tool for new players. At least I would think so. Nonetheless do a lot of people join into mine.
Spamming in map chat just isn't my thing to be honest, but reason I did make this guild now is maybe one day become a reffered-to place if people ask for help, and so becoming a kinda intuitive way for new players.
Also there arent really any other ways, and not all people will straight away go to forums/reddit etc for information, so I want to keep it as much InGame as possible.
On the "Joing groups to help with Achievments"
The project is more based around helping with questions and guiding people to the sources where they can find the right information rather then directly pulling people through troubling content, although I do that too (Just went through PoF Maps twice today to help 2 people get their first elite).
That's the spirit, more is always welcome of course.
A guild only for F2P Players doesnt make too much sense I guess. I don't exclude F2P and I don't see a good reason why I would exclude others specifically.