Personally I don't think you need to have the basics...

{of stuff like "...alternate picking, legato, arpeggios, scales and what else is needed to become a solid lead guitarist..." } 

...down BEFORE you start learning to play your favorite songs.

Many people use the parts of songs to develop those skills.

However...
What I think you - and everyone; who wants to play guitar - needs is:

{a fundamental understanding of how to make music with guitar}

Lots of people learn scales and chords and etc... but they can't actually make music; because they don't understand all the flashy licks and solos in context of the fundamentals.

so my advice

1: commit to a course that takes you through the fundamentals

2: learn the songs you want to play
(free tempo) 
Don't try and play that stuff seriously until you can play all the exercises in the fundamentals course PERFECTLY with ease.

3: Start playing with other people ASAP

Anders is a working professional musician
Which is why I think Guitar Tricks Fundamentals 1 & 2 will give you good foundation.
He knows what you REALLY need to know and do in order to be a competent musician.