Distance from lamp should be about good coverage across entire canopy. Intensity of light should be about DLI. If you have to favor one or the other, focus on hitting proper DLI. 100w probably only going to cover 3-4 sq ft (depends on efficacy of light)... a bit more if you stick to autoflowers, because you don't need to run on a 12 hour schedule. Don't bite off more than you can chew. you'll just end up with a bunch of larf.
Water like you would any standard potted plant. Marijuana isn't special in that regard. The only caveat is whether you are using 'soil' fertilizer or a soilless/hydro setup.
-With soil you want some mininmal runoff to ensure full saturation, but not wasting your soil's nutrients...
How often you fertilize depends on concentration of your feed and how you need to supplement that particular soil product over time. Some personal preference.. but the more often you add it, the lower the concentration you need, obviously.
-With soilless you want 10% runoff or more every irrigation, religiously, and always fertilize with a well-balanced diet.
I suggest treating it like a soilless medium. check out cocoforcannabis.com -- it doesn'tmatter if it's coco or not.. soilless is soilless if the medium is constituted properly. Soilless is the shortest learning curve, imo. If you have a good formula and stick to the required runoff, you are basically guaranteed good results without knowing much.