and technically it is "kits" simply because he does sell pre assembled single cob engines. and due to the nature of cobs being able to be driven at many different loads, thus making you choose your own driver. (which as amazing as cobby is, leaves recommendations for almost what ever you want to build) so its easy to match what you want to do.
weve all been in your shoes, we all were new at some point. so feel free to ask questions. this is a forum, and were here to talk and help.
and cobby always includes hardware, screws/nuts/eye bolts. its great.
just remember that he does have the pre built engines. and you can always use it as a blueprint to piece together your own. and its always nice to have everything you need in one easy spot. as shipping adds up fast across multiple other distributors due to the semi heavy nature of most of these parts.
but imho its totally worth it. even and cool light, customize-able, efficient, what you spend on hid bulbs every six months you could buy one or even two single engines, 4 to 8 1212's, 1 or 2 1825's and if you use the iceled heatsinks, you get a duo top canopy fan (which are amazing) what you are spending on expensive hoods, lots of ventilation, bulbs, electricity, and in some cases co2 supplementation, typically destroys the the upfront cost of building, in comparison.
when you buy a prebuilt fixture expect to spend 2$ per wall watt for good quality.
when you build, expect to pay .50c per wall watt for exceptional quality.