Reminder - As it is possible preorders for some or all devices may go live this week - Put money in your steam wallets.
I think its likely the review embargo for the steam controller is lifting this week based on the leaked early review and valve's unlisted "unboxing" video. At a minimum, its probably the controller. Whether or not we get dates on the Machine or the Frame, its a good idea to put some money in your wallet now.
If this release is anything like valve's other releases, the will probably open pre-orders either right after the release date and price reveal, if not very shortly after.
I suspect you'll need a steam account with some minimum account age. If they go with the 5 dollar preorder route like they have with other devices, you may experience difficulty getting your order in before they sell out. The bottleneck is always the credit card transactions. If you already load the money in advanced, you'll be one of the first in line.
I'm putting 25 dollars in my steam account just to be safe.