I have been to the US multiple times with a B1-Business Visa and didn't do any of this stuff. I just showed up and the customs officer asked a bunch of questions about my purpose of visit and that's about it. I didn't need any invitation letter or hotel bookings, etc.
Hotel bookings and a LOT of other documentation is required when applying for a tourist / business visa for Europe or UK, but traveling to the US has always been fairly straightforward (except that you need to make two visits the US embassy or consulate twice for the visa formalities).
At all times, I had my company laptop with all the data + source code.
Is this something that has recently begun?