1. You can use playlistType=rolling to limit the number of files stored. You need to specify also the number of files in playlistLength parameter. These parameters are added in the createHLSStream or createDASHStream command. Note that the number of files stored will still be not equal to the playlistLength because of the staleRetentionCount which defaults to some number. You can set this value also and add it as a parameter.
2. The default behavior of createDASHStream is it generates live profile. If you want to be able to seek to a duration, then you need to instruct it to create a VOD by specifying dynamicProfile=0 as a parameter to create DASHStream. If you do this, and you want all the source stream to be viewable. Make sure that the playlistType=appending, if you use a rolling playlist. It will still generate a seekable VOD but only for the part covered by the playlistLength.
3. I guess you issued the pullStream command first before the createHLSStream/createDASHStream that’s why you missed the few seconds of the video. You simply have to reverse the order of the command. Issue createXXXStream command first then pullStream second.