Clubs first. Balls just burn your credits, clubs don't. But wait until you level up enough until you can get some decent clubs, and use this time to build up a nice stash of credits from all the free offers. L48 R1 driver is very good, L48 Max slow irons are OK or L58 G20 irons are good. Max spin wedges will also allow you to play with cheap or free balls and still be able to get some spin and control on shots. L55 Rossa is cheap enough to be a good buy until you are able to get one of the higher level putters.
You will pick up some free balls from WGT along the way just for playing in certain comps or on promotional days.