ISDN was pretty much plug and play when I had it back in the day. The gateways were available off the shelf (IIRC mine came from CompUSA) and you could get them with either one or two B channels, as I recall.
Yes indeed. I had the pleasure to work for Ascend Communications for 4 years. The bulk of our business was the Ascend Max TNT that could terminate dozens of PRI lines into hundreds of digital modems. They were the bread and butter for early ISPs. For BRI lines, there was the Pipeline 50, remarkable little box with a BRI input and Ethernet output. Good times.