How to do incremental / differential backup every hour in Postgres 9.1?

Trying to do an hourly hot incremental backup of a single postgres server
(windows).

I have the following setup in postgresql.conf:

max_wal_senders=2
wal_level=archive
archive_mode=on
archive_command='copy "%p" "c:\\postgres\\archive\\%f"'
I did a base backup with pg_basebackup -U postgres -D ..\archive -Ft -l
2013-07-07 -x

Which made a big base.tar file in the archive folder and added some long
file name files, which I assume are the WALs.

pg_start_backup('label') and pg_stop_backup() seem to create the WAL files
in xp_log, and then copy them to the archive folder.

Questions:

1. what command(s) do I run to do a new incremental backup (pg_basebackup
does a new base backup which I don't want right now)? do I just run select
pg_start_backup('label'); select pg_stop_backup(); on a schedule?

2. What does the label in pg_basebackup and pg_start_backup() do exactly?

3. WAL Files don't seem to be removed from pg_xlog. What should I do about
that? It seems to keep 5 or so WALs in pg_xlog. Is that to be expected?

4. Do I need to backup the .backup files in the archive folder or just the
16,384KB WAL files?

5. should I use the --xlog parameter and if so do I need to change
wal_keep_segments from 0?

Thanks!

Neil