Like Jason I don't believe snow will be much of an issue.
Not sure if I understand your question regarding Fantail. Ropers HSR traverses above Fantail and goes to Spuller just as you describe. Fantail is a nice enough lake, but it does have a trail leading to it. If you want to remain off-trail in the back country it makes sense to bypass it.
Have you read Roper's short article describing the exact trip you are planning: http://www.gorp.com/parks-guide/travel-ta-yosemite-hiking-family-camping-sidwcmdev_053972.html
This is a fantastic mostly off-trail trip. Many of the lakes including Gaylor, Cascade, McCabe, and Youngs have trails to them so while the route is mostly off-trail, it isn't quite as remote as he describes.