Totally agree with Betsy in how to approach this. A typed up plan might be taken the wrong way even if you are both good friends. What usually has happened with the organist(s) I work with frequently, I at first just let them open up the opportunity for me to make a suggestion. Sometimes, it’s as easy as them asking me, “So, what would you like to do for this Sunday/funeral/wedding, etc.?” Other times, one of the organists I work with will say something like, “I’m having a difficult time finding a hymn for Offertory/Communion/Recessional, etc.” So, I take the opportunity to make a suggestion. I’ll be like, “Oooo… How about “insert title”? That would work perfectly for this week.” Of course, in order for these organists to get this comfortable with me, we had to get to know each other and they had to see that I had no intention of trying to either “usurp” or make them feel like they aren’t doing their job well. Actually, those particular organists usually have wonderful choices and really understand what is needed for liturgy, so there isn’t a problem there. BUT, even with organists and other instrumentalists who may not either have the experience or the best taste, etc. I’ve learned to be able to work well with them to a point where they feel comfortable asking me for a suggestion and even using my suggestion, even though we may not always see eye to eye in regards to liturgical music. I just treat them with respect and they appreciate that, just as I appreciate them treating me with respect.
Anyway, I think you’ll be fine with your organist friend.