learn to sew, it's great to be able to make your own clothes and costumes or adapt things that don't fit perfectly. sewing is a quite manly skill, it's not just something that mothers do. with some sense of shape and a tiny bit of perfectionism, it would be almost impossible to do it wrong.
any clothes that fit your waist are good. the waist is a terrible hassle to adapt, legs are easy. so easy you only need to know how to thread a needle or use a sewing machine. long sewing courses aren't needed.