What Dale said is true. The replicator database and the replicator itself are 2 different entities.

Yes, but only when certain configurable conditions are met (fragmentation level, time period). There's some user level documentation in the default.ini config file:

https://github.com/couchbase/couchdb/blob/preview/etc/couchd...

ok, that would still lead to a situation where my server crawls to a halt for hours and might never finish if I don't basically take it offline :(

The next major version of Couchbase will have that feature, amongst many others (the alpha release already has it in fact).