Hi Dave!
I'm afraid I can offer nothing to directly aid you in caring for and then releasing your dear (if not "dear" now, it will be by the time you finish) little squirrel -- because I have no experience with them, beyond maintaining and stocking separate feeders in the yard to keep them and the birds happy.
I can offer buckets of moral support. I've lived the bulk of my life near a riverfront recreational corridor and various wildlife sanctuaries, and I swear...the animals put up signs saying "This way to Danneaux's --> Good Food and a Warm Heart Await". Everything from winded baby bats to injured hummingbirds, frozen flickers, and tiny oppossums and raccoons arrived with regularity. The parents of a nestful of swallows co-opted my services and deputized me as Official Collector for restoring the kids to the nest when independent, successful flight was yet a dream for the little ones. I finally left the ladder out front in the driveway for the whole season 'cos I got tired of lugging it in and out of the garage every 15 minutes when the parents screamed for help and the neighbor cats drew near.
All my wildlife encounters were brief; the animals either died from injuries before I could enlist the services of a vet or recovered quickly and fully and left on their own after a brief recovery. The many domestic cats and dogs dumped and abandoned by thoughtless owners who ceased caring for them were a longer-term commitment, as they often required nursing care, re-socialization after becoming feral, and then placement in responsible, caring homes for their remaining lifetimes.
The one caution I would offer is to check early to make sure you are authorized to provide care to a wild animal. Here in the States, laws vary by municipality, state, region, and at the national level as to who can rightfully care for wildlife. Locally, we have a number of authorized agencies, non-profits, and people "deputized" to work for them in rehabilitating wildlife (sadly, comparatively few such agencies exist for domestic animals in need). That said, I know any number of people who have rehabilitated wildlife, and a recent acquaintance who hand-raised a wild squirrel with complete success -- and also successfully released it afterwards to live a full and happy life on its own, back in the wild. My own reaction is if the squirrel is of the same type as others in the immediate area, there isn't much difference between you raising and releasing it and what would have happened naturally -- the grown squirrel would still live in the same area, no matter what parenting it received. Some animals simply "fall through the cracks" in wildlife laws, and then it is up to individual efforts if they are to survive and recover. It is no small thing you're doing, Dave, and I think the experience will touch your life in a positive way pretty much forever.
If you've managed to keep the little squirrel going for a couple weeks already, I'd say you're doing everything "right" with regard to the actual care you're providing. Well done!
All the best,
Dan.