I'm not a tax attorney, but generally it's recommended that business and personal expenses and equipment be separated. If it's combined, I think in some cases you can claim by percentage, like home offices can be claimed by square footage. If you get audited, you'll have to prove its primary purpose and usage is business.
Without doing any research I'd probably aim to build something akin to the OpenPandora.
3d print a 3ds like case for a pi. Use a hat to connect all the knobs and buttons. A little fan to keep it cool. Should be more than capable of playing old console games.