The only civ I trust to maintain a declared friendship without DoWing on me, at this point, is Sumeria. Everyone else, a DoF seems to be an invitation to DoW.
On the other hand, I finally gave in to my annoyance and converted Delhi (and all of India, for that matter) to Eastern Orthodoxy. So now crazy Ghandi is spamming Orthodoxy missionaries. So far he seems to only be using them for scouting, but its a breath of fresh air. The opportunity cost? Losing out on a chain of some of the best Great Persons the world has ever seen. Did you know there is an engineer that increases the production and RANGE of all of the buildings in a district?
As an aside note, I believe that if you purchase multiple apostles in the same turn, they will get the same promotions. At least that was my experience several turns in a row.