So I am still trying to figure out how to get 12 or more feats as per the Mailman build and I am a bit bummed that DFAs at the highest level only get 8 invocations known total. With a Pixie that woul max at 7...why do Warlocks get so many more?
Because Warlocks need invocations to alter their Eldritch Blast, with their Eldritch Essence and Shaping invocations.
That only leaves a certain amount of non-EB invocations for general use.
Compare that to the DFA, who uses different Breath Effects for the same purpose.
Both classes gains things that modify their main attack method -EB and BW- and they gain aprox. the same amount of "general" invocations.
I'm not familiar with the mailman sorcerer, do you have a link?
There are no PrC's for DFA the way HfW is for Warlock as far as I know.
The only thing I know if is the Heir of Siberys PrC in Eberron Campaign Setting, but that requires you to be one of a few races capable of possessing Dragonmarks. Pixies aren't one of them.
The thing is to take at least 1 level in it and then take the Breath of Siberys feat from Dragonmarked, granting an additional 2d6 to your breath weapon. But that is a moot point in this case.
Besides fivefolded breath of tiamat is better than a normal Hellfire Blast, at least without ... unsavory
tricks to increase it.
Another divine casting class could get you ED, but that would require 3 levels and net you less powerful spells compared to the Ur-Priest. So you could, but it's not a good idea.
There is a more optimal order to take your levels in the sneak attack build, if you want Daring Outlaw earlier.
I say so since it requires 2d6 sneak which you won't get until your 8th class level.
There might be some BAB problems, but it might also not. Depends on how many attacks you want to gain and if you use Partial BAB, an optional rule from
Unearthed ArcanaWithout them, your BAB is 12.
With them, your BAB is 13, only one point of difference.
With all the various attack bonii one can aquire, the only real difference between different levels of BAB is if you have more or equal/less than 10 and more or equal/less than 15.
Since you won't be acheving BAB 16 for that additional attack, it makes little difference in having BAB 12 or 13.
I hope that answers at least one of your questions.