Buying gear can be a slippery slope, especially if you start doing it at a fairly low level. For instance, once you buy your first good putter you'll want to get the higher level version when you advance a few levels. And sometimes there will be an even higher level option.
Similar with irons and, well, all clubs really.
I'd wait until you can buy gear that will last you a long time, you'll save a lot of credits doing it that way. If you really want an improvement on the starter gear then perhaps you could consider the King Cobra F8 iron set, only 325 credits and will be a big improvement. The clubs you use most are your irons so I'd advise you to start out by replacing them.