Ok, mostly looking good (though I'll leave spec comments to a more experienced fire mage).
Big thing that I noticed with a) your trinket and b) one of your rings. I know these are hard items to find usually, but strength, attack power and hit rating do nothing for you as as mage (although hit and crit rating are being changed to work for both melee attacks and spells soon, but currently there is a seperate spell hit/spell crit for casters).
Soon you can do the questline in Felwood/Winterspring for the Timbermaw and at the end you can get
Power of the High Chief as a reward.
Also, as you're an alchemist it may be worth making/equipping your
Philosopher's Stone (recipe from Alchemist Pestlezugg in Gadgetzan), the strength and agility won't be of any benefit, but you'll get use out of the stam/int/spi on it.
Soon you'll get more items available with spell damage/spell crit (and stam/int aswell) so those will be good to pick up.
About the threat, best bet is to give your tank a little time to build up some threat before you start attacking, also starting with a scorch or two before fireballing can help. You might want to get a threat meter (omen is one of the more popular ones), if your tank has a threat meter installed then you will see a bar for the tanks threat on your target and a bar for your threat. Keep your bar below the tanks and you should be ok.