Is this sweater warm enough for winter?

Yes for indoor and mild outdoor wear. Cashmere insulates well for its weight, but the crewneck and fine knit suit layering under a coat rather than replacing one.

How should I wash it?

Hand wash cold with a cashmere shampoo or dry clean, then dry flat. Do not bleach, and avoid hanging it, which stretches the shoulders.

Does it fit true to size?

Tom Ford knitwear tends to run close to the body with a trim shoulder. If you want a looser layer over a shirt, consider sizing up.

Will the ivory color show stains?

Yes. Light cashmere picks up marks from coffee, food and deodorant, so spot clean quickly and keep it away from dark denim and rough outerwear.

Is it worth it over a cheaper cashmere crewneck?

The difference is yarn grade, softness and finishing, which you feel rather than see. If you want one plain sweater that lasts and drapes well, it earns its place; if you want visible design, look elsewhere.