Sounds gorgeous! A jumper of that vintage will NOT be shrinkproofed, so machine washing and drying is out of the question. Hand wash only in lux flakes or a very gentle wool wash (half strength) in lukewarm water. Rinse well twice in lukewarm water. Roll in a towel and press out excess moisture, and dry flat in the shade. Patting it into shape on a dry towel helps it keep its shape while drying. If it warps a bit, pin into place on the towel just like blocking a handknitted piece before assembly.

A teaspoonful of miscible eucalyptus or lavender oil in the second rinse water will help to keep moths away. Fortunately it may only need washing occasionally - wearing a shirt underneath will do a lot to keep it clean.

Mending is best done with darning wool if you can find any and if you can't then embroidery/tapestry wool is probably the next best choice. You might like to reinforce cuffs and collar on the reverse side with a split strand of matching wool a few millimetres in from the edge to help stop fraying. Wool lasts very well when cared for, but can get a bit fragile at the edges when those edges are stretched. If there's a ribbed edge, then both top and bottom of the ribbed section benefit from that extra strand of wool - does a lot to help it keep its shape while still allowing it to stretch appropriately.