When stable is ahead, you should still get all the updates on the beta channel.

By what metric? It was never intended to complete with consoles on price to performance.

For PCs, have you seen the price of components? 16GB of DDR5 is already around 200 USD for the very cheapest options, and a 512 GB M.2 NVME drive is around 90 USD. There is no way that, with the current market, you can buy or build a 400 USD PC that has specs anywhere close to the Steam Machine. Speculative/rumored prices are similar to what you could get for a similar spec mini PC.

No, Valve’s rule is that you can’t sell Steam keys at a lower price in different places. You can sell the game at any other price without the potentially-unlimited Steam keys they provide to devs.

Steam key rules and guidelines in the Steamworks docs: https://partner.steamgames.com/doc/features/keys#3