What steps are needed to stream RTSP from FFmpeg?

You can use FFserver to stream a video using RTSP.

Just change console syntax to something like this:

ffmpeg -i space.mp4 -vcodec libx264 -tune zerolatency -crf 18 http://localhost:1234/feed1.ffm

Create a ffserver.config file (sample) where you declare HTTPPort, RTSPPort and SDP stream. Your config file could look like this (some important stuff might be missing):

HTTPPort 1234
RTSPPort 1235

<Feed feed1.ffm>
        File /tmp/feed1.ffm
        FileMaxSize 2M
        ACL allow 127.0.0.1
</Feed>

<Stream test1.sdp>
    Feed feed1.ffm
    Format rtp
    Noaudio
    VideoCodec libx264
    AVOptionVideo flags +global_header
    AVOptionVideo me_range 16
    AVOptionVideo qdiff 4
    AVOptionVideo qmin 10
    AVOptionVideo qmax 51
    ACL allow 192.168.0.0 192.168.255.255
</Stream>

With such setup you can watch the stream with i.e. VLC by typing:

rtsp://192.168.0.xxx:1235/test1.sdp

Here is the FFserver documentation.