Yes, ESTATE is a Scrabble word!

Letter values in Scrabble US: E 1, S 1, T 1, A 1, T 1, E 1.

Is it a valid word?

ESTATE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

everything you own; all of your assets (whether real property or personal property) and liabilities
extensive landed property (especially in the country) retained by the owner for his own use
a major social class or order of persons regarded collectively as part of the body politic of the country (especially in the United Kingdom) and formerly possessing distinct political rights

Also: landed estate, estate of the realm, the three estates.