I seriously don't know. I think you might want to feed it something mice would like
5 week old mice should not be eating milk. They should be eating adult ouse/rat food by the time they are 3 weeks old.
it take a week
There may be nothing wrong with them. There just may be too many for the mother mouse to feed. Pet mice do not do as well as wild mice when little. Keep an eye on the mom to make sure she stays long enough with the kits to feed them good.
a milk
Only feeder mice, but if you really wanted to you could keep a 3 week old feeder mouse as a pet
No!
No, they get their fur in time. About 3 weeks with the mice I had once.
Around $1.50. For live mice it cost 3 bucks. If you want a corn snake, you only have to feed it once a week! But that adds up! ($310.00 a year!)
Three times a day
Mice are slowly weaned by their mother at 3-4 weeks old.
90 to feed a family of 3 for a week => 30 to feed one for a week => 30*5 to feed a family of 5 for a week ie 150. However, this assumes that it costs the same to feed adults and children in a family (unlikely), and that there are no economies of scale (also unlikely).
2-3 pinkie mice in one meal - once a week.