i'm not master tailor, but i think i can answer your questions. ^_^
Q: when will i be able to make
green items?
A: i believe the
brown linen robe at tailoring lvl 30 is the first
green item you can make. i think the
spidersilk boots at tailoring skill 125 are the first
blue item you can make.
Q: will it cost me more if i make them
green?
A: in general, yes, but sometimes not by too much. at higher levels though, yes,
green items tend to need extra thread or colored dyes or more cloth than non-green items.
Q: can i find recepies for tailoring from drops or i have to buy em all?
A: both. you can find dropped recipes and buy plenty from the tailoring trainers.
- on the disenchanting, that's currently the route i'm taking (tailor/enchantor). i just recently (at lvl 26 warlock) stopped disenchanting every green item i got (aside from what i could use of course) and have started selling some of them. i have my enchanting at 121 and am needing reagents that i'm not getting from the stuff i disenchant. i use thottbot.com to check what an item will disenchant into and if it's not something i need, i'll sell/AH it instead of disenchanting it.
hope that helps.