I think the list is pretty good, although there are some areas which could be improved, but I'm not convinced by the plan you have for using some of your units, particularly the Dire Avengers, is going to work well, so I have a number of suggestions to make regarding both the list, and the strategy.
Guide seems pretty redundant in this list, so I suggest replacing it with Doom, which is going to benefit your scoring units much more in experience.
Your Guardians lack protection on foot, and I have found that two units of these are better than one, so I suggest dropping the Jetbikes, taking a second Guardian Defender squad, replacing the Spiritseers with Warlocks (assuming you take two units), and then add assault protection to your infantry section, in order to prevent your opponent from employing a break out strategy and smashing through your Guardians in an assault.
To this end, I recommend adding Striking Scorpions, and, if you can find the necessary points, pinning Dire Avengers as well, so that you have both an offensive and defensive infantry line, which also gives you more options in terms of your choice of strategy.
The Fire Dragon squad does not really need an Exarch for tank hunting in my opinion, so you could just field six regular Dragons, while I feel that their Serpent would be better off being equipped with a Shuriken Cannon, since if you mount a weapon with anti-tank potential on a Wave Serpent transporting Fire Dragons, it tends to make them even more of a fire magnet, as your opponent is likely to seize the chance to shoot down two anti-tank options with one shot.
Warp Spiders make for a good link between the mechanised and infantry elements, but may need to be dropped, so that you can bolster other elements of this list. If you do decide to keep them, then I recommend dropping Withdraw, as this unit isn't large enough to be assaulting anyone in my opinion.
Anti-tank Wraithlords are only effective when fielded in pairs in my experience, so I strongly suggest taking a second one. If you do so, you could then downgrade the Brightlance to a Shuriken Cannon on your Dire Avenger squad's Wave Serpent. You may have to drop the War Walkers to accommodate the second Wraithlord, especially if you bolster your infantry section as I have outlined above.
I'm concerned about your strategy. You have a lot of units being used independently when they need to be used interdependently. The mechanised wing is a prime example of this, since, for such a wing to be effective, I have found that all the units need to disembark in a position to attack at the same time, otherwise your attack is too easily halted, and your squads can be picked off piecemeal. For this reason, using the Dire Avengers in the way in which you described is not a good idea, as they will be needed to support the Fire Dragons.
Overall, you are off to a solid start with this list, but I feel that a few tweaks need to be made, particularly to strengthen the infantry section, and that you strategy could do with being altered somewhat, in order to make better use of the type of army you are proposing to field.
I hope that helps.