Yes, the CH is easy to shoot down if you have AA guns, however the helldrake can't do much against the CH as it's focus is on ground targets, so you should focus on downing that ork flyers first if it is a fighter, if it's a bomber then the CH will be quite safe. The autarch will also be great help to the CH, since you will want it to have the first blood in the airfight.
If you do not take the CH I would recommend taking lances on the walkers, just in case there is a landraider or similar around.
concerning DE:
I wonder how you are going to fit the kabalites in the FD-serpent as they cannot start in it, since it's a dedicated transport.
However may I suggest that you use the archon to deepstrike the firedragons, and then give the serpent to the guardians, granting OS to the serpent. the 6 kabalites would have to be on foot or maybe you can fit something else in.
3 reavers could be a great swap, I've use reavers as a good bodyguard for a bikeseer, it grants the farseer hit & run and with the right drugs the unit is T5.
Those kabalites in the raider are really good against MC, and with splinter racks quite ok against FMC.
concerning Tau:
The FW are awesome behind cover, to bad tau are not BB anymore, otherwise you could take a "batman" with the reapers for special rules goodies. So unless you are taking a larger TAU allies I'd suggest the fireblade or an ethereal.
You could use Tau for AA though, either by taking an AA riptide or AA unit of broadsides with missile drones.
Another good tactic is to try to match-up the warp spiders against chaos soulgrinders, due to the soulgrinders low Initiative.