I am thinking of playing one in an upcoming game. It seems fun but I am not so sure on the tower shield it is affordable at low level but it takes away from your ability to do damage especially at lower levels. What I got so far is Marytr and Good blessings race either Human or aasimar. I am completely lost as to what feats to take. I don't see any way to remove the -2 to attack from tower shield as I said so I don't know if it is worth going down that path. I was thinking Divine favor and cure light wounds as prepared 1st level spells. 15 point buy is what I think the game will have so in order am thinking 15,12,14,10,14,7 Aasimar making the wis as high as it ever needs to be before items and making the dump cha less bad. If human probably still put the stat in wisdom to get more uses out of fervor at 2nd.
You don't have to use a tower shield with it. It's an option, that's all. A heavy shield is likely a better option.
The bigger problem with the archetype is that you have far too many uses for your swift action. Starting sacred shield, directing it to protect someone else, and of course casting spells with fervor. If you do use a tower shield and go down the mobile fortress style feat line (the main reason for using a tower shield IMO) then you'll have even more uses for swift actions. You get just one swift or immediate action per round.
If you use a heavy shield then the theme of the archetype would support getting the combat reflexes & bodyguard feats. Or you could just get the usual combat feats - power attack etc.
How high level is your campaign likely to go?
As I said in the archetype guide a while back, it's a definite step down from a standard warpriest. It's also a step to the side though and could support a front line character better than a standard warpriest if you'd rather not play a frontliner yourself.
I'm iffy about trying to write general optimisation guides. There's many which are essentially an attempt to justify or promote the author's preferred character build, and even with the best of intentions they tend to be too general to be useful or too specific to help the particular person asking.