Spiro doesn't have any effect on breast growth per se. If used alone, by blocking the effects of testosterone, it might clear the way for the little natural estradiol males have to produce minimal, usually slow, breast growth, but, yeah.
Anyway, testosterone is a "dominant" hormone. If you take estradiol alone, its effects are going to be greatly diminished by the presence of a lot of testosterone, probably. That's why anti-androgens are so effective. They clear the way for estradiol to act.
About the order, uhm, yes, some endocrinologists prescribe anti-androgens before estradiol. Sometimes, they try estradiol alone first (since by itself it acts as a weak anti-androgen and in some cases it can suffice). And sometimes, they prescribe both at the same time. It's all about the endo's beliefs and the patient's hormone levels, I guess.
I should say though that using an anti-androgen for a long time (many months or years) without taking estradiol can be bad for your health.
