For just a couple billion rows and a dozen joins, a single node will suffice (with the caveat that you really want at least 3 nodes because CockroachDB is built for replication and fault-tolerance and you're not getting that with a single node cluster), but you'll get linear speedup as you add more machines.
Your performance on a single node should be on the same order of magnitude as doing this in Postgres right now. We are rapidly closing that gap, and intend to close it completely for TPC-H style queries, while retaining the linear performance speedup with more nodes.
The reason this gap isn't already closed is we've been focused on transactional performance in distributed, fault-tolerant situations rather than analytics performance, for 1.0. There are lots of optimization low hanging fruit that we haven't focused on in analytics scenarios that we are just getting started on.