I grew up with Jerseys and my Mom still milks about 60 to 80 head but mostly Holstein cattle now.
You already know that Jersey's tend to be more sensitive and temperamental than most other breeds. The fence line contact idea is worth a try and I think it most likely will work but be sure the fence is in decent shape an have some sort of plan B just in case. At 9 months of age the yearning to get back to their moms may be more of a companionship urge as anything else. As for returning the heifers back in, I think 3 or 4 weeks should be plenty long enough.
For the extended milking: In the old days the ideal lactation cycle was 305 days milking and 60 days dry before calving. Most people were able to hold close to that back then but current economic conditions have made hash of it. 380 day lactations with 20 days dry is not uncommon. My mom has made the point that it SEEMS to not to hurt the cows but I wonder about the long term health effects of doing this over and over. Keep in mind she has mostly Holsteins. I don't think Jerseys are able to handle that much physical stress of milking and carrying a baby calf at he same time. I do believe that your plan of extending the lactation period in order to have a better calving date is fine and good, but I also believe that a 50 to 60 day dry spell before calving would be well deserved. After that I would try to stick to the old 365 day lactation cycle. To me that seems much more natural and is should result in healthier cows and calves as well as better milk production.
I like the feed ration even though I have no experience with feeding sunflower seeds to cows. I think it has a good balance of protein and energy for volume of milk and good butter fat content. Although you may already know this, the feed ration has quite a bit of influence on the make up of the milk. Most commercial dairy rations tend to have a lot of protein because they are geared to Holstein cattle and for high volume of milk with a 3 to 3.5% butter fat content. For Jerseys I would back off the protein to 16% and up the energy content. The best ration I have ever seen for Jerseys took advantage of their ability to produce a rich milk with very high butter fat. It was about 35 - 40% alfalfa, 35-40% ear corn (corn on cob still in the husk), oats, sea mineral, and molasses, The milk was sweet and the butterfat content was unreal. I do grass feed beef but I have no idea how well grass feed dairy would do. I would like to see you results because yo may be on to something.