First of all welcome to a much bigger pool of fish. As a long time player of this game, despite my moniker and picture I actually used to be a Akuma/Sagat main in vanilla SF4. I will be going very in depth so if you skim it and see I go into small intricate things that seem obvious I apologize, I’m just trying to help. 
i hope it doesn’t suck as i am new at this.
First step is finding a character and looks like you have the makings of a ken player,
as he pretty much covers your checklist of preferential tools.
aggro style? check
combos? A plethora of listed combos are available here on Shoryuken forums.
projectile to keep spacing? also check.
Momochi japans best(lol fanboy much eh gaiz?). has a whole video series on this guy on Youtube.
Ken also covers somewhat of your defensive needs as he has safe moves and average health.
Moving on to the way to get good at this game…Well practice just like all fighting games you need to find like minded individuals to practice with. but there is also what you have to practice. You won’t know until you start playing and start losing. As losing in fighting games is the only way to move forward and improve. then there is rage do not let this grip you as you will only become blinded and never get better due to the rage hazing you, keeping you from seeing your flaws and thus improving them. You have to actually want it and this will be a much bigger pool of players of all different backgrounds and ability. So to finalize this part DO NOT BE AFRAID OR ANGERED DUE TO FAILURE.
Next from what i can help you with is game mechanical differences. Meter or bar in this game is different from UMVC3 and Skullgirls. from my understanding in Skullgirls you can whiff or hit a normal attack out of range to gain meter. This is not the case in street fighter 4, in SF4 you gain meter only from landing attacks. Blocked attacks will give less meter but some none the less. Special moves are the same as Skullgirls you gain a bit from just using it.
As you can see if you have played at all, you will notice their are two bars of meter in this game (three if your a smart ass and count the health “BAR”) That are both your Super combo and ultra revenge combo. Both have their own utilities that are part of this iteration of street fighter’s mechanics.
The super meter in this game is your resource pool, you need it for almost everything. In SF4 you will use your super meter are used for many things including: super combos, EX specials, and Focus Attack Dash Cancels. The super meter is comprised of 4 segments in this single bar when full, you can cash them all out and use a super combo for big damage.
More traditionally though it is used for safety mechanics like FADC which will cost two segments and can reset your character to the focus/saving attack that you can then cancel to a dash in this game, which I will get into next in this guide(?).
on the flip side of that for more damage and combos it is common to use a single segment and use a EX special they usually provide better advantage in some way (damage/priority increase)
the ultra meter is built up from taking damage from your opponent and is a “comeback” mechanic, much like X-factor but not as extreme. think of it as a high risk damage move as usually the drawbacks (frame advantage/properties) are big to match the damage payout.
Onward to the focus attack, which is done by holding both the medium attack buttons. When done your character will charge up a attack that has three stages. releasing the buttons will cause the attack to execute. You can also dash forward or backward during any point except for stage three if it does not connect on block or hit. Dashing during these earlier stages will cancel the attack and just dash instead allowing you a full reset your character considering how you use it of course.
one is the basic hit does small damage with little to no hit stun.
two your character will flash white signaling you reached the stage two focus attack this block able attack has medium damage and causes a “crumple state” in this state they freeze in place and fall to their knockdown state at a slowed state this can be canceled into a dash to continue the punishment of the one who has been hit with this. In addition to this when you reach any stage of focus you gain one focus armor. This allows you to absorb one hit and still continue the attack, or even dash out of it for safety. Be warned though, their are armor breaking attacks that will break the armor and dish out full damage. The absorbed hit will effect your health but it will reduce it to “grey” recoverable over time health.
lastly to stage three you holding down this long means usually that they are either stunned or not paying attention or did a bad slow move that had no armor break. Either way this is bad for them as it has the same “crumple state” from the stage two but they fall much slower to knockdown state allowing a bigger window for damage. along with this it deals the maximum damage available for focus attacks and is unblockable and an armor break.
I’ll be constantly editing this and now I kinda want to make a few videos I have a lot of spare time. If you have any more questions even ones not pertaining to these insights ask away I will do my best to answer. I’m sure some stuff is confusing I have a hard time getting words out to say what I mean like even now ARGHHHH. Any who good luck on your way to becoming a great street fighter player and I might even see you in tourney!
i hope it doesn’t suck as i am new at this.
it is HOLY HELL 6 am goodnight me.