PITR question with base backup

I'm in the process of testing PITR recovery, and I have an issue.

My "data" directory is 30GB. Not huge, but it certainly takes awhile to tar
up.

My understanding is:
a) pg_start_backup
b) tar up
c) pg_stop_backup
d) restore tar file

The problem is that I create databases pretty regularly. Let's say I create
3 in a week. I'm not looking forward to going to my colo, grabbing the 20ish
GB tgz file and restoring it 3 times per week. I'd rather do that dance
monthly or quarterly and rely on the WALs in the interim.

So...can I:

a) pg_start_backup
b) tar up my data dir
c) pg_stop_backup
d) restore
e) WALs are all happy
f) Day 2 - create new db
g) pg_start_backup
h) JUST grab the data/base directory for the new db
i) pg_stop_backup

move on?

What about "global" or "pg_clog" or "pg_multixact" or "pg_tblspc" and
"pg_twophase?"

I don't _think_ I would ever want clog, but maybe I'm wrong.

Is this possible, or do I absolutely need an entire new backup of the whole
data dir?