I recently came back after a loooong time, and doing some slayer atm. But as the whole combat triangle changed, and prayer, and weakneses etc, im confused.

Im supposed to do a Spiritual Mages task now, but it seems to me that they use Magic, yet acording to http://runescape.wikia.com/wiki/Spiritual_mage/Strategies i should go with Melee defense if i decide to Melee them? Why not ranged gear, (Like Dhide)

Range gear will reduce melee accuracy, so it's not a good idea to mismatch gear like that. However, right now, gloves, boots, and helmet slots don't interfere with accuracy, so you can use range gear in those slots to provide some magic defense if need be.

Range gear will reduce melee accuracy, so it's not a good idea to mismatch gear like that. However, right now, gloves, boots, and helmet slots don't interfere with accuracy, so you can use range gear in those slots to provide some magic defense if need be.

Well, for the helm, i got a 2 times upgraded Slayer Helm, for a cloak I have Trimmed Attack cape, and for gloves i got them Barrow gloves (Recipe for disaster)

Those aren't bad choices. You could wear Glaiven Boots for a bit of extra Magic def, as they're Ranged class, and don't interfere with your accuracy, as said, but they're far from significant.

 

Spiritual Mages seem to have fairly low Defence overall anyway, but you could always just range them as intended. Alternatively, you could permanently block them from being assigned, as they're not very good for XP or drops, unless you're seeking Warpriest gear.