Nah, you may not be a n00b, but you've a bit to learn, as you've admitted yourself. First off, welcome to the Guard forum, I'll be your local Moddissar that, despite his hiatus, seems to be on often enough anyways nowadays....
Storm Trooper Squads
Cameleoline/Carapace Armour (Depends on mission)
Light Infantry (Debating wheter to take this off for Iron Discipline)
CLose Order Drill
First off, not many spots of your list actually state any Doctrines that you've taken, so I have no idea how many points you've spent on your Doctrines, and how ingrained in the list each of them are.
Second, some of these choices are suspect.
Storm Troopers: A buyback, so it makes sense as you do want them
Camo: With Catachan models, this does make sense, in a way. With "camo clothing" and incredible skill. Though keep in mind that camo is a special equipment docrine, and as such must be given to EVERY model that even has the option of taking it, no debate.
Carapace: On Catachan models? No way. As it is a special equipment doctrine, every guard infantry model must take it. Catachan models don't look like they even have Flak armour, let alone Carapace. Take a look at Storm Troopers. THAT'S Carapace. How can you warrant Catachan models having Carapace armour? Not even the regular plastic Cadians have Carapace. I'm afraid you won't be able to use Carapace with Catachan models.
LIght Infantry: Makes sense with Catachan models. Though, you cannot take it when you have Carapace (Or vica versa). You've also made a mistake on how Light Infantry works later on, but I'll get to that later.
Sharpshooters: Statistically proven to be a waste of points in most situations. Fortunately, not EVERY squad has to take this, like the special equipment doctrine. Though most people feel that unless you can warrant it with the history of your regiment, you're better off without it.
Close Order Drill: Combined with Light Infantry or Camo? It makes no sense. Yes, it's free, yes it can be useful in the right situation, but it makes no sense with the doctrines you've chosen so far.
Command Platoon "White"
Led by Senior Officer (Some really old Catachan HQ model i have laying around...)
-Boltgun (Codex says i cant have this though?)/Power Fist
1 plasma, 3 Guardsmen with Rocket Launcher
1 Commissar with CC weapon and Bolt Pistol (Is it just me or do these guys really suck now)
Boltguns are bolters, so it's the same thing. However, the Power Fist is a waste on your Senior. It'll likely go like this: *Assault/be assaulted, Senior officer readies power fist. SO dies, powerfist goes to waste*. Keep in mind that your Officers are independent characters, meaning the enemy can pick them out in combat, meaning a powerfist equipped Officer becomes one huge powersinking target.
Now, reconsidering this, you think Commissars are useless? Not so. Give HIM the Power Fist! Commissars are not independent characters, meaning that the enemy will have to chew through the other guardsmen to get to him, giving him plenty of time to swing that power fist. Commissars are some of your best close combat specialists because of this fact. They lost an attack in the new Codex, yes, but that doesn't make them useless.
3 LasCannon teams with Sharpshooters
Probably the only spot Sharpshooters is useful in. LasCannons with Sharpshooters is questionable, but Heavy Bolters gain a huge benefit from it.
Grey Knight Hero with Thunder Hammer and Shield
5 Grey Knight Terminator Retinue all with Standerd Equip (Nemises Weapon and Storm bolter)
I don't use Grey Knights, so I can't comment on their effectiveness. Frankly, I don't need singularly powerful models to win games for me. Just a guardsman with a gun and some guts behind it.
Storm Trooper Squad #1 (attached Chimera)
1 flamer, rest hellguns
Storm Trooper Squad #2
1 Grenade Lauchner, rest Hellguns
No real comment here, though they could be a bit better....
Grey Knight Terminators
4 terms with 1 Brother-Captain, 1 incinerator
See comments on your Grey Knight HQ.
Junior Officer, with CC weapon/bolt pistol, 2 guardsmen and flamer
You forgot to account for some Guardsmen here. Seems like you only have 3 or 4 models, when it's a squad of 5. Otherwise, it's okay, if you intend to move it up with the rest of your flamer equipped infantry squads.
9 Guardsmen and 1 Serg.; 1 flamer
9 Guardsmen, 1 serg.; 1 grenade launcher, 1 autocannon
9 Guardsmen, 1 Seg.; 1 Flamer, 1 lascannon
Fine here. Massed cheap lasgun fire is never to be balked at (Unless you are the opponent). The squads equipped with heavy weapons can just be used with the rest of your firebase. However, the last squad there is questionable for a couple reasons
1) The LasCannon is a long ranged anti-tank weapon. The Flamer a short ranged anti-infantry. They don't match up well. You run the risk of firing the LasCannon at a heavy target, wasting the rest of the squad, including the Flamer, or running forward, wasting the exorbitant cost of the LasCannon, which brings me to point 2:
2) A LasCannon in a squad of infantry is so expensive it's almost not worth it. You're better off just taking a Missile Launcher and saving the points. With the LasCannon, it does have the benefit of being behind a buffer of 9 infantry, yes, so harder to dig out. Though if you are firing at big targets with it, as it was intended, you waste the rest of the squad. If you use the squad to fire against infantry, the LasCannon is ineffective. Though a single squad with a LasCannon is hardly crippling to your army, you'll probably want to avoid equipping too many regular infantry squads with LasCannons.
Junior Officer, CC weapon/Bolt pistol
3 guardsmen, 1 meltagun
This squad, like the last one, is designed to move forward with your assault elements. You leave the problem of "What will I do with my firebase if my officers are all moving forward?" I'd take the LasCannon out of the infantry squad above and put it into one of your Command Sections to use as a firebase anchor.
9 Guardsmen & 1 Sergeant; 1 Flamer, 1 Rocket Launcher.
9 Guardsmen & 1 Sergeant; 1 Flamer, 1 Heavy Bolter.
9 Guardsmen & 1 Sergeant; 1 Flamer, 1 Sniper, 1 Heavy Bolter.
9 Guardsmen & 1 Sergeant; 1 Sniper, 1 Grenade Launcher, 1 Heavy Bolter.
9 Guardsmen & 1 Sergeant; 1 Sniper, 1 Autocannon.
9 Guardsmen & 1 Sergeant; 1 Grenade Launcher, 1 Autocannon.
Here is where you made your mistake with the use of Light Infantry. The Light Infantry doctrine allows you to take a sniper rifle in your infantry squads. Though that's not the right wording. It allows you to effectively replace the heavy weapons team to take a Sniper Rifle equipped Guardsman. As such, you have three squads that have taken the sniper rifle (Also note that you did not mention that you took Light infantry in those squads either), and yet you have taken a heavy weapon for each as well. You will have to remove either the sniper rifle, or the heavy weapon.
Otherwise, the squads are fine. A good firebase.
1 Sentinal Squad (1 with Lascannon and 1 with hvy flamer)
Fine here. However, you are probably better off splitting those Sentinels. That way they can move and fire independently. Sure, you lose the benefit of a single buffer vehicle against fire, it doesn't exactly help that much (Especially when it's entirely possible for a single volley of fire to take out both vehicles without problem.
(3x) Leman Russ with all upgrades
What, exactly, constitutes "All upgrades"? Because some things that could be considered in "all upgrades" could be considered a waste of points. I can't help you if you don't tell us.
The tactics you intend to use with this list are fine. Adapt to the enemy, of course, but otherwise, you're fine.
You said this is 3400 points? Or is it less? It sounds like less, because you don't exactly have a large army there... Other than that, there is not much more I can say....