That should work fine. Be forewarned that it can be tough to find the low level availability for the domestic segments on DL that work with your connections. If you are in business/first, and you can't find one of the domestic segments at low, you can always do it in Y if it's available at low.

Also note that JFK-SFO will never price at low level in business, as it is DL's premium transcon route with business elite service. It will always price at medium or high miles and drive up the price of your trip. Economy on that route can be had for low miles. Flying via FCO-LAX usually has great availability in J, and then it's a short 1h flight up to SFO which typically has good availability in both F and Y with many flight options.

You can't have more than 8 segments, so also keep that in mind. I am not sure if that means 4 outbound and 4 return max, but I think you could do 3 segments oubound and 5 segments return, so long as the total is not over 8. Some of the others here would know more (3cforme or mtkeller perhaps?).

You can also do an open jaw and stopover. So if you can't find low miles on some of the domestic segments, you could just purchase a revenue ticket. For example do EU-CDG-JFK <open jaw> SFO-DTW-RDU-(stopover)-JFK-EU and then purchase a one way JFK-SFO ticket. That route is usually fairly inexpensive in Y, and you'd have to get all your bags in JFK to clear customs already, so not too tough to recheck for the continuation flight. Heck, you could even turn that into a few night stopover in New York too :-)