Hey, I teach a lot of beginners, and everybody starts the same way. Learning big open chord shapes, songs, or scales/reading music/theory stuff. Both of those ways are really hard to start playing guitar.
I found a better way...
I wrote a cool book with specially designed songs that are very short and very cool, basically just excerpts from the real deal. I'll walk you through the first few pages:
1. Love Somebody (maroon 5) - 1 finger song on 1 string. cool tune, easy to understand how tab works
2. Hypnotize (system of a down) - STRING SKIPPING song, works on developing your picking accuracy and moving 1 finger along the first string every couple times.
3. The Simpsons - using 3 fingers and 3 strings, making sure that you can use your fingers independently
4. Star Wars - 4 fingers and 4 strings, a little bit harder, but still extremely easy
5. Whats My Age Again (blink 182) - another string skipping pattern with 1 finger
6. 3-string open chords - you can play most of these with 1 or 2 fingers.
These songs are super easy and even an 8 year old girl can play them quite perfectly on the first try. You can too. :)
So check out my book if you want to see these songs!
[PM me if you want a link - you can view the first 10 pages for FREE]
Notice how I focus a lot on PICKING and FINGER INDEPENDENCE on the first few songs, and then start with SMALL CHORD SHAPES.
The SMALL CHORD SHAPES are very important. Most people start with super hard chords like the big G and C chords, and when that doesn't work they get frustrated and give up.
This page kind of demonstrates what im talking about:
http://www.music-for-music-teachers.com/images/480xNxguitar-chords-little.gif.pagespeed.ic.4-DlS3UGNq.png
Some of the chords can be played with just 1 finger. Learn those chords. They sound exactly the same as the full shape and are way easier to start with.
As far as mastery goes, you should score yourself on 1-10 on each lesson. As long as you can score like a 7 or so, you should be fine to move on. That's like a C+ B-
The thing about music is that as you learn more things, the previous materials become easier to play.
Like if you are working on a 1-string song.. you don't really have to spend hours trying to get it right because the NEXT song is a 2-string song...
...and guess what, you're ALSO working on 1-string as you're doing the 2-string song. so why should you focus on mastering the first one?