I started out on full doses of both E and Spiro, and HRT has definitely been very kind to me, so yeah, nothing to worry about.
I also have friends who started off on almost nothing, on low-dose E alone for months, then low-dose Spiro, and it took like 2 years for them to get their hormone levels into the female range, and yet they feminized just fine, so seriously, I don't think it really matters that much, I think it's all down to doctor preference.
I dealt with some nasty mood swings in the first couple of months that my friends didn't get due to the rapid change in hormone levels, which is probably why a lot of doctors like to ease into it, but it worked out.