I'm not a combat master like some people on here, but I'll be glad to tell you how I handle things. A dual-wielding rogue is actually my favorite build in DAO, and I favor it over the dual-wield rogue in DA2. One of the coolest things about the DAO dual-wielder is that you don't have to use two daggers. You can actually use a one-handed sword and a dagger from the beginning of the game (giving you more damage than just two daggers), and if you upgrade the dual-wield tree to "Dual Mastery" (I think that's what it's called), you can actually wield two one-handed swords, thereby completely eliminating the need for daggers and greatly increasing your damage. Wielding two big swords (like Starfang and Blightblood or Duncan's sword and Maric's sword) make your possible damage higher than pretty much anyone else's.
1) For your companions' tactics, I usually set them at "aggressive" or "ranged" depending on their build, then set them as either "defender" (for tanks), "scrapper" (for damage dealers) or "archer." When it comes to mages, it depends. I usually set Wynne to "healer" and Morrigan usually as "damager" or "debilitator." After that, I see what the game sets for their tactics, and then alter them if I don't like them. I hate micro-managing, and most of the time, if I do these steps, I don't have to take control of the companions, unless I want them to do something very specific (like "revival" for Wynne).
2) Alistair is definitely your best tank, but you can make Sten, Oghren, or Shale tanks as well. Just set your tank's tactics to "defender." Two-handed weapon users like Oghren and Sten usually have two sustained modes that they can use to alter their fighting style: "Indomitable" is usually used by defenders, and "Powerful Swings" is used by scrappers. If you read the description of each ability, you'll see why. Make sure if you use one of them as a tank that you give them some constitution points, as they often don't start with the best constitution stats for tanking (particularly Sten because you get him so early).
If you are playing on the PC, I would suggest using the Character Respec mod to completely respec Leliana and Zevran, as their defaults often aren't the greatest. Leliana is a good archer (set her to "ranged" and "archer"), but Zevran's default specifications kind of suck, in my opinion. But since you are playing a rogue, if you don't bring one of them along, you can unlock doors/chests and spring traps yourself.
Wynne is an excellent healer, and I very rarely die when she's in my party. I rarely die anyway, but she makes it much better, and she keeps the other companions alive longer. Morrigan can do a great deal of damage, but it depends on what spells you give her and how you set up her tactics. I would suggest making sure you get "Crushing Prison" with her, as that spell is a killer.
Dog is actually a pretty good companion, particularly his "overwhelm" ability, which is where he can knock people down and shred them to ribbons. If you are on the PC, I'd recommend the Extra Dog Slot mod, which gives you the ability to have Dog as an extra party member at all times (he fills up the slot a ranger uses for their wolf, bear, spider).
Shale is a pretty awesome companion. She actually has four modes she can use: scrapper, defender, ranged, and a support mode (fourth line on her tree). Plus, I adore her personality.
3) The Ranger spec is quite nice, and each of the pets have their own strengths/weaknesses. They are all better once you max out the tree because they all become "corrupted" versions of themselves. As for using them, I honestly just summon the best one for the situation and let them do their thing. I would suggest summoning each of them at some point when you're not in combat, take control of them, and then see what talents they have. That will help you determine when the best time is to use each.
4) As for poisons, I usually only use them on bosses. The cool thing is that you can double up on poisons. I took out the Broodmother yesterday and had four different poisons on my weapons at the same time. She went down fairly quickly. Each poison will tell you what kind of damage they do, and they will also tell you if they do mild, moderate, or potent damage. Choose the one appropriate for the situation.
I do not use traps. I hate them, so I can't really advise you there.
As for the balms, you have to decide when to use them based on the situation. Like for the High Dragon "Andraste," use the warmth balms, as she does fire damage. For the "Archdemon," use spirit balms, because he does a lot of spirit damage (most darkspawn do spirit damage). I use the nature balms in the Brecilian Forest if things get hairy. I have never used the ice or grounding balms, because I've never needed them. There just aren't a lot of big bads that do ice or electricity damage. Swift salves are great for bosses or really large groups of enemies because they greatly speed up your movement, so you can do more damage faster. I don't use Rock salves because I don't like how slow it makes you, and I've never really used the Incense of Awareness.
I hope that helps!