if you have other LFS in your area, i would definately switch. the one you are using seems to be in it for the money and not the welfare of what they sell, or the welfare of you. i dont know what kind of questions you had asked previous to making your purchases (if any at all), but i dont think they were looking out for your wellbeing. assuming that you would have asked any questions, i would hope that they got the feeling that you as a consumer, were new to this, and they should have been more helpful or started with baby steps
i personally suggest doing some learning on the nitrogen cycle. before you buy any other livestock, learn what their specific requirements are. it wouldnt surprise me if that same shop tries to sell you something that isnt compatible. since you are in deep on the reef stuff, i would suggest watching videos (many videos) on reefs for beginners.
if it all dies off while you are waiting for the proper supplies, my suggestion would then to be to restart, and start slow. instead of jumping into a reef tank, start with fish first. thats just my opinion, so take it for what its worth. at this point, i would also stop taking any suggestions from that LFS or take what they say with a grain of salt, and research by asking here, or looking online to confirm that their word is good