If the baby is moving around with mom on steady legs and the weather is not horrible, snow, hail, etc. you can let them out any time. Though if this ewe is a wild one it may help to keep her in the stall for a few days, 3 or so, and do some hand feeding of grain to tame her down. Not for the lamb's sake though.
I have used this tactic before it can help.
My ewes lamb out in the pasture and I bring them into the barn only if there are problems. Low milk, lamb not keeping up, bonding issues...
You can castrate at any time. Just depends on what method you are using. With banding when they are to big for the bander then you need to find another way. But I know people who have castrated 3 and 4 year old rams.
There are several reasons to keep a wether. They can act as teasers and bring your girls in to heat earlier. Not a real issues with hair sheep and they have to be castrated a special way for this to work.
For 4H, FFA, youth projects. Or just for a pet lawn mower. I sell a lot of castrated lambs as pets. More than ewes. Don't know why.. I just do.
Just remember the longer you wait the harder on the animal it is.