I don't know how open you'll be to my advice but I'll try and help.
If you have no issues germinating seeds then that's fine, but regardless I would recommend a thermostatically controlled heat mat. It helps to get the temp in the exact correct range for seeds and cuttings and brings up the germination and cutting strike rate to close to 100% (with seeds this depends if they're viable in the first place though, obviously). You move the Root Riot cubes (made by Fleximix) into the system when you see lots of roots coming out the sides.
If I were you I'd ditch the plan of growing in diatomite pebbles completely as that idea as described is a non-starter. I would look into as simple a way to grow as possible so you can get used to the whole process. Growing in compost would be best but if you're set on hydroponics, coco would be ideal for a beginner. You'll need a pH pen and I would recommend Hesi coco bloom which you can use in the vegetative stage and the flowering stage. I wouldn't recommend DWC for a beginner because it's very fiddly and plants are more prone to massive nutrient deficiencies than other systems.
If you want to go down the DWC route you should use hydroton/LECA (expanded clay pebbles - see pic below by clicking on nsfw tab). They have to be prepared in a certain way by first running tap water through them for ages and then soaking in pH adjusted water overnight. You put it in a net pot in a hole cut in the lid and fill the bucket with pH adjusted nutrient solution with an air stone which bubbles nutrient water up onto the roots.
As for the light, it depends on how much weed you want. If it's just for yourself, I would recommend using a 400W-600W HPS in veg and bloom. I wouldn't bother with CFLs or fluorescent lights if you worried about cost, because the 600W HPS in particular is the most efficient growing light in existence and will produce the most bud per killowatt-hour of electricity consumed. The optimum amount of light to use in any given space is 50W per square foot of floor space, so a 600W lamp will light a 1m x 1m space (3.28 feet x 3.28 feet). Likewise a 400w HPS will light an 0.86m x 0.86m space (2.83 feet x 2.83 feet).
You
need to have proper ventilation. I assume you've sorted that out? It's
not optional. Not only will it supply the plants with fresh air containing sufficient carbon dioxide for essential photosynthesis to take place, but it will also remove heat produced by the light, and believe me they produce a lot of heat. For a 600W HPS lamp you would ideally use something like a 6" high powered Ruck which is 725m3/h as the intake and the same as the extraction. You would slow down the intake to have slight negative pressure so all the air will go through your carbon filter, which leads me on to my next point.
You
need a carbon filter. Again, it's not optional. It will stink not only your whole house out, but likely your whole street. I've known a whole street to be filled with sweet skunky cannabis odor with just a single plant someone was growing, and yes, they did get busted in the end. The smell from a flowering cannabis plant seems to even permeate through brick walls. If you're doing a tiny little micro grow in your bedroom if you live with your parents or something then you might get away with it for a while but anything more substantial and you will get caught.
