What a unique quilt. I would SITD and just do a simple crosshatch on the calendars. I would not do any FMQ on them at all. A 1" crosshatch grid, either on point or not would be keeping in the vintage look of them and it would not detract from the wonderful graphics on them. I agree using a neutral cream thread and would probably go with an finer thread like Superior's bottom line or So Fine. Then you could do FMQ in the borders and sashings. I have found that a sage green color seems to go with everything.