What's next?

You can do a lot with major minor and seventh chords. make sure you know what a sus chord is

on lead start with the pentatonic scale and then the major scale

but you also need to think about what kind of music you want to play

if blues or jazz then your 9ths may come in handy

however if you are going for straight ahead rock then think about powerchords instead

good luck

Huh?

I've seen a chord chart for a Major 9th and it looks nothing like a Major 7th. Or maybe I'm looking at the wrong chart.

A7 = x02020 notes played are A E G C# and E
A9 = x02423 notes played are A E B C# and G

Pick up your guitar and play each of these chords. The difference is not irrelevant. The notes are not the same. They may be in continuum with a sequence but there is a noticable diffence in the sound of the chord. Example,  If I need to play  A7 in a song A9 will work , and it will , in most cases, enhance the song. But if I need to play A9 in a song and play A7 it will , again in most cases, sound empty and lacking.

No, no, no brother dude the last is not irrelevant. The last E is the accent on the chord. It's the final note that gives the chord its distinction. And I'm not sure where you're getting this stuff but if I play an A7 when I'm supposed to play A13 on , lets say Steely Dans' Deacon Blues, bottom line, it's gonna sound lacking and incomplete. Again here the note that changes the A7 to A13, the one you say is irrelevent, is the accent note, the note that differentiates one hearing the song and saying, "hey i know that song" or not playing the accent and have people say " what in  the hell is he playing?"

again my archaic artifact chords;
A7 = x02020<accenting defining final note in chord sequence
A13=575657<this little B here seperates, accents, and defines the chord
                          and if the person playing beside me doesn't play the specific
                           chords I chart for them, I find someone who does.

If you're saying that my A13( 575657) is incorrect then your dispute is not with me but with Donald Fagen , Walter Becker, Larry Carlton, Lee Rienour, Wayne Shorter, and Chuck Rainey straight out of the Steely Dan songbook(Aja). I  have, and continue to learn a great deal of my theory from these guys and I mean you no ill will nor disrespect but I'm gonna give more legitimacy to Fagen, Becker and friends than you. I admire your passion nontheless.
  I don't think you and I could co-exist in a band together. (haha)

Now I do realize that theory is important and I work a bit on studying something new every week, but damn, it seems like you theorists want to take all the fun out of music. Reminds me of first year college calculus, and I don't ever want to relive that experience!

There should be some kind of rule, like the sum of the chord fingering cannot exceed a total of 10 or something (barre chords excluded), I mean what the hell is an A13 (575657), LOL

Glad you asked! 

A 13 chord is an extended 7th, derived by adding the next appropriate member of the triad.

So for example, if we take the A major scale, for two octaves.

A B C#  D  E F#  G#  A  B  C#  D  E F#  G#  A

Now lets assign each note of that two octave spread a number.  The first you'll know, as they're the common "Nashville numbers."

A B C#  D  E F#  G#  A  B  C#  D  E    F#  G#  A
1 2  3    4   5 6    7     8  9  10   11 12  13   14  15

So, to build a normal major chord, we take the 1, 3, and 5 notes of the scale.

A  C#  E

To build a 7 (or dom7) we take the flattened 7th (maj7 would be the unmodified 7th.)

So A7 is

A  C#  E  G

Want to build a 9?  Simply add the 9th note (which is really the 2, but we're another octave up now).

A  C#  E  G  B

11th?  Piece of cake.

A  C#   E  G  B  D

13th?  No problem.  You know what to do.   At this point, you've got every note in the scale in the chord.  That's why you never see an A15 chord.  The "15" is already represented in the chord, so you'll be repeating yourself.

A  C#  E  G  B  D  F#

In all of those cases it's the 7th that sets the tonality of the chord.  (dom, maj, diminsihed, etc).  The addition of the extended notes merely adds color to them.  It doesn't change the fact that they're still 7ths.

So thats what the hell a 13 is.   

Theory is what makes music fun.  It's the glue that holds the notes together to make music.  Random notes is just noise.  Put them in some kind of framework, and you get art.

Jerome, I understand what you're saying, but... 

The way I learned it, is that there are 5 (and only 5) 7th chords:  Major 7, minor 7, dominant 7, diminished 7, and minor 7b5.  That's all the ways that you can make a 7th with 4 fretting fingers.

Now, I would agree with you that 9th's, 11th's and 13th's are "built on" 7th's in the same way that the 7th's are "built on" majors: you include the previous added notes.  But I would disagree with the terminology that 9th's etc. "are just" 7th's.

I also know that we both mean the same thing, it's just a difference in how we choose to say it.  You say Tomato, I say tomahto.