Hiya, don't know how much help I'll be but I'm happy to offer my perspective.
I first picked up Dragon Age a year ago and have since play Origins and DA2 3 times each (have just started DA:I)
Classes - I've played so far...a dual wielding rogue, an archer rogue and a two-handed warrior. Archer rogue and two-handed warrior have the same flaw, in that they both run out of spells 2/3 of the way thru so you can't get really really strong at either. They both bored the crap outta me as they had so few things to do and I was just standing there most of the time.
I'd go with a dual wielding rogue as you can survey the battle, watching what your companions are doing (and controlling them if needed) then strike when it suits you. For me at least it lended itself to more of a team fight than just focusing on myself, while still letting me just play my character if I felt like it and be all swishy swishy ninja murder knife and whatnot.
As a tank you'll be stuck in the middle with no idea what the mages are doing further away so, if you want a little micro-managing, maybe not the best idea.
Make the effort to learn the basics of what your companions can do so you can fully understand and make use of the tactics section (obviously, but duh...it took me ages to do that haha)
And as for me I vary my team all the time, I never have just 3 ppl. I always mix it up and use all different combos. This is especially awesome in Origins as it gives you great banter between them all. Recruit everyone if you're only playing once, there are some great conversations and opportunities so don't walk away from any potential companion.
DLC's - Return to Ostagar is a favourite for me, nostalgic feelings from the battle. I like leaving it till late in the game, recruiting Loghain, and taking him with.
Warden's Keep - Meh. It's okay but the story isn't exciting for me. You could totally just watch it on Youtube or read up on it to make your keep choices.
Leliana's Song - Fun, not necessary tho. Also goes against the lore from Origins which bothers me, re-writes some of her history :/
Witch Hunt - Boring. Watch the last 2 minutes on Youtube, but otherwise nope.
Shale - Awesome. Freaking awesome. Talk to her as much as you can, she's a peach.
Darkspawn Chronicles - Still traumatised tbh....oh god.....the carnage.
Awakenings - In the minority here, I hate it but others love it.
If you get bored 2/3 of the way thru, then I suggest ignoring all small side quests. Stick to the main stuff to shorten the playthru. None of it is important, but you could be guided by the Keep. So when you're in Orzammar, check what's in the Keep and just do that stuff, ignore the rest etc etc. You could pick up as many as you want but only complete what's convenient and don't go off for an hour trying to find a little thing for example. I managed to avoid all the Dalish side quests for instance, by siding with the werewolves and killing them all! So, you know, that was handy 
The zones are level specific tho the game doesn't tell you that. So it's Redcliffe and/or Mages Tower first, then to the Brecillian Forest, then Orzammar/Urn of Sacred Ashes, then Denerim (tho you can go to Denerim any time you like for other stuff, but killing will be harder there)
Mods - Now if you're on PC there are a couple of mods you should really get, all from Nexus mods. If you don't know them I'll list them...
Extra dog slot - allowing dog to be, well, in a fifth slot so you still get 3 companions with you.
Skip the Fade - some ppl hate that section of the Mage's tower so it skips straight to the boss fight, keeping all loot and perks you would have gotten if you'd done it
Morrigan Restoration Patch - restores some of her dialogue that got cut
A Year with Sten - I chose a face for Sten here, and it links to another patch that makes all Qunari in the game look like the DA2 Qunari. Works great and is good for continuity between the games
Zevran ASAP - Gets Zevran after you leave Lothering, instead of much much later in the game.
There's also the ZDF Dialogue Fix and Improved Atmosphere. They're fantastic, highly recommended, but they're big and take a little effort to get them to work together. I managed it tho so it can't be that hard.
I can also recommend some for DA2 (including this crucial one for the plot flags importing over - DA2 Import Fixes ) if you want, and some for Origins to vastly improve the Alistair romance should you be doing that.
Character - As for story I've just played my third world and damn it was great. It's a pro-Templar world where I make every choice against magic that I can. Now i expected to hate it, to be a big bad magic hating Nazi ******...but it was awesome. I started with a dwarf noble. Didn't fancy being a dwarf tbh but the Origin is really good. I played her as a plucky little dwarf who loved fighting, and never had an arguement that couldn't be won with a punch in the face. She was blunt, terrible at diplomacy and a bit thick, but loyal, passionate, hornyhornyhorny, and always tried to help. She saved Loghain, Alistair ended up in exile, so to expand on that I got to the Landsmeet asap so that Loghain could travel with me as I finished up extra quests and DLCs. I did a Zevran romance which I wasn't in to I have to say. Thought he was creepy but went with it and it was so so good. Totally recommend it, or if not try a Morrigan romance. I haven't done that yet but it is, or so I've heard, super tied in with everything and really good too.
That's a theme of this world (I have 4 DA worlds). Yes my protagonists want to help, so they're good people, but my dwarf warden, then Hawke, then dwarf Inquisitor all have an attitude of 'if there's a spider on the wall, go get a huge old mallet and whack the little bugger. Sure, the wall falls down and the pipes burst, but hey! I got the spider!'
That's how I play that world and it's so much fun. Blunt, to the point, companions rolling their eyes in the background, but eventually they love me anyways despite my bull in a china shop demeanor. I'll work with shady ppl, give them a second chance (Sten, Loghain etc.) be respectful to the Chantry but all mages are probably dodgy so better safe then sorry.
Both my warden and Hawke in that world are dwarves because I find it much easier to be anti-magic as a dwarf. A human would be anti-magic out of hate or fear, but my dwarves just. don't. get. it. It's weird surfacer hinky sparklyness that makes them feel odd and they don't like it, so better safe than sorry. They respect the Templars and the shitty job they must do and help them with it, and are guided by them. So anti-magic. And it actually worked out great.
Went sword and shield Templar warrior with Hawke. She was aggressive/sarcastic, had a rivalry with Varric and Isabela which were SO good. It was dodgy with both till act 3 then when you get 100% rivalry you end up best mates. I know, doesn't sound like it makes sense but it did. Best friends with Aveline and Fenris. Ignored Anders and Merrill entirely. Ended up loving this Hawke to bits which surprised me. She was pro-templar throughout, tho she did save Bethany at the end cause she didn't hate magic, just BLOOD magic.
I hope some of that rambling is helpful. I'm not all about the best specs, is all about characters for me, but maybe there are a couple of useful tips in there for you.
Good luck 