Dual-wielding you throw both weapons, and the weapon thrown will be at random, with the occasional time where both of them are thrown at once;
You gain global effects (eg Resistances) from both of them at all times, but on-hit effects (eg Attack Damage Converted to Health from the weapon) are only triggered when the weapon itself is used;
Throwing weapons work to proc both the Rune tree and the Warrior tree. Throwing weapon warrior mixes are an incredibly potent build set basis for physical throwing weapon builds (for Int conversion builds, just use Rune).
I also had a quick look at your Steam post. Maxing primary resists is always a good start, but beyond that, the best defence becomes a strong offence, particularly on mid-Epic and Legendary. At higher levels, enemies will simply overpower you, and if you can’t put them down rapidly they’ll swarm and overwhelm you. Don’t worry about maxing physical and secondary resists, it’s very difficult to do and you won’t face enemies with each secondary resist enough to be worth it.
Dodge/Avoid attacks are cool, but very difficult to stack, and if you can get to the max of 80%, the cost of capping it will be that the attacks that do get through could one-hit you. Have a bit if you want, but don’t max it.
Defensive and Offensive Ability, however, are super important. With low DA, enemies will always Crit you, and with low OA, you’ll never hit enemies. In general, physical attackers should go 1:1 Str/Dex, while Int users should go 2:1 Int/Dex, with the occasional health points sprinkled in.
In conclusion, good DA and near-maxed primary resists is enough defensive-wise. These are all my own opinions, and others please do feel free to correct me, but I think the only viable defensive build is damage reflect Evoker. With Icescale armour and Athena’s Shield and the Dream perks, you can create a viable reflected that can melt mobs without attacking. Super OP (apparently), but massively gear dependent. There are a lot of videos on YouTube you could check out.
Hope that helps!