Don't buy anything. Just ride what you've got and build your skills and experience until you can make your own decision.
You will quickly get to a point where you can rip on the gear you have and see the things you are missing out on and then you can decide on the direction you want to go and the gear you need to get there. (ie. waves, slalom, freestyle, etc)
You've only been going for 3-4 weeks so you have barely begun. There's heaps of stuff to learn and plenty of time.
Avoid the temptation of getting a mongrel collection of gear that doesn't work together. Plan your purchases and buy stuff that works as a system and helps progress you.
It's probably best to think about your rig before you spend too much money on boards. A decent set of sails with matching mast and boom can be used with multiple boards.
There are massive bargains to be had in second hand gear. There's heaps of guys selling full quivers ... because they've switched to kiteboarding and they don't need all that stuff anymore.

[}:)]