I'm about to get back into the Mojave and would like some feedback on what I should specialize in. I want to be a swift talking gunslinger. I'd like to specialize in all kinds of weapons from Heavy to Energy.

In that case I recommend Speech, Guns and Energy Weapons.

Tag Skills: Speech, Guns, Energy Weapons

Traits: Skilled, Hoarder

Recommended Perks: Cowboy, Gunslinger, Terrifying Presence, Quick Draw, Plasma Spaz, Laser Commander, Grunt, Travel Light

Recommended Armor: Light armor

What is "Tag" skills? Should I side with NCR or House?

Tag Skills are the three skills that you choose at the beginning of the game, and basically, in the modern games, that just means that they start out 15 skill points higher than your other, non-tagged skills. Role-Playing wise, you can stick to your Tag Skills at first, i.e. if you tagged Guns, Barter, and Repair, then you would focus your level-up skill points on those until they are maxed out.

As for which faction? That's up to you. You have the choice of siding with either House, NCR, Legion, or Yes Man (independent) in this game. So the main questline breaks into four different questlines right after you complete Act 1. I don't want to influence your opinion before you have the chance to try everything for yourself, so just choose which faction you think is best then go from there. If their quests start making you do things you don't like, then you can always revert back to the Yes Man/Independent questline and finish the game that way. But yeah, it takes at least 4-5 playthroughs to really experience the game in full, or at least to experience the main quest in full.

If I tag Speech, Guns, and Energy Weapons will I be screwed if I want to be skilled in repairing and crafting?

What SPECIAL traits should I focus. I want to be good with all gun types and a really good talker.

No, you can still easily raise repair, survival, and science (crafting skills) even if you don't tag them. And that goes for all skills; Tag Skills aren't that important in Fallout: New Vegas, except for role-playing purposes as I mentioned before.

Agility and Charisma are important for characters who use Guns and Speech, but Strength is important for every weapon type, so make sure that is at a decent level too. Perception is good for snipers, since a higher Perception allows you to detect enemies at longer ranges. Luck is also important for Guns skill characters (very important imo) because it raises your critical chance. Read about critical hits http://fallout.wikia.com/wiki/Critical_Hit, and know that with some Guns skill weapons, you can critically hit someone 95% of the time. And also keep in mind that every sneak attack you perform (that's when you attack someone when you are in [Hidden] status) results in a critical hit.

http://fallout.wikia.com/wiki/Critical_Chance

Thanks a lot

I always just tag speech, lockpick and guns.