Sorry I was gone a few days.
Anyways it sounds like you have had some good advice -- One thing that I would keep in mind though, is that other than for expense, you cant have too much footer for a colomn. IMHO 12" posts look pretty cheezy and spindly when done -- I think you would be happier with 16" or larger columns. with 12" columns you end up with a 4" x 4" hole in the center and it takes four brick per course, but by going to 16" you get and 8" x 8" hole down the center which is four times better than the 4" x 4" one for only two more brick a course.
As I said before you want as big a footer as you can afford -- your gonna be putting a lot more money above the ground than under it so don't scimp here.
I would go at least twice as big for the footer too, and at least a foot deep. and have at least four pieces of #4 bar laid out in there like tic tac toe spread a little more to the outsides but still in from edges too half way down in the mud. Any additional size or thickness will be to your advantage too. I would then have a piece or two of #5 bar sticking up out of footer at least 32" for lap high in the center ( spread a little) and more bar to drop in the hole when you are done with the columns that reaches from the top of the footer to a few inches from the top (one or two of these should do) of the column.
Then I would pour them solid full of grout ( wet concrete) when joints were all set and take the additional bar that you are going to stab in the grout and pump them up and down several times to settle grout.
Brick are not strong for fence structures and neither is the mortar between then -- 95% of your strength should come from the reinforced concrete inside of them -- and any kind of anchor attachment should reach well into that as well.
With 12" columns or posts you get so little of that that it hardly counts. Wind is hard on fences, and even if you have one that doesn't catch wind, like wroght iron, it will look better and last much longer with beefy columns.
Don't be surprised though if you can go out in several years and see some settling has taken place -- it shouldn't be too bad, but you will probably be able to sight down the fence and not see a perfectly straight line at the tops of columns anymore -- they all do that sooner or later, depending on soil and grade situations (geomorphology). None of us live or build on hard solid ground, it is more like building on a raft -- in your case several rafts tethered together
, so a little movement will come along, just make them as strong of individual rafts as you can.
Oh BTW I didn't understand what you were going to do with the 4"s (4"x8"x16") but you don't want to use two of those if you can use one 8" (8"x 8" x 16") you want the big holes in 8"s for the same reason -- the strength does not come from the mortar between blocks -- it comes from the reinforced concrete in the holes -- Block are just pieces of form that doesn't need taken down, 95% of the strength is what goes in those holes.
I hope that helps and gives you some things to think about.
Jacques
