Welcome to the forum!
There are a few home-school parents on the forum who should be able to field most of your questions.
From this thread:
http://talk.collegeconfidential.com/prep-school-parents/1624008-updated-bs-parent-resources-p5.html
mountainhiker and classicalmama are home-school parents
Regarding the two schools mentioned in your post…for someone who does not have a child at the school, I am an Emma Willard superfan. Am familiar with both Porters (daughter did summer program there) and EW (daughter applied and was admitted) out of the “usual suspects” girls schools and prefer EW.
This thread, from my older daughter’s process may be worth reading…covers a lot of the process, and many of the schools mentioned on this forum: