I have made all of my equipment from reading about the techniques and build ideas from the DIY guru's on the forum and every time I brew I always seem to want to add some more to the mix. But my best piece of equipment (or part really) was the sight tubes. These little pieces of Polycarbonate have made the process of water transfer and measuring so much easier and opened up to scrutiny the liquor volumes and boil losses and mash tun losses I now feel confident with any brew I do. So in answer to your question. Most kit out there will be fine providing they are large enough to handle your desired batch sizes, but make sure you have sight tubes on your HLT/Boiler.
PS. Decent temperature gauges are also high on that list as well