The Best Combo in FFXIV
First, mining + blacksmithing. There is a BIG problem with that plan: to make anything out of ore you need fire CRYSTALS, not shards. And in my experience, fire crystals are extremely rare, at least for the first 15 levels of the game. I don't think I found even one so far. So you'll be digging up ores that you can't synth into nuggets, which means you have to buy all your nuggets to skill up, which means Buy FFXIV Gil. Maybe it will be different on retail, or maybe there's some trick to getting fire crystals I don't know about, but in my experience, blacksmithing and armoring are the WORST starting crafts.
The best combo is probably botany + weaving. Using your scythe you can harvest all the fibers you want, turn them into thread, and turn those into cloth. And you can do it using relatively common shard types like wind and earth. Carpentry also stacks up well with botany but there's not much you can use carpentry for without needing another craft skill. With weaving, you can generally turn what you harvest into saleable gear without needing much extra skill. The only caveat is clothing that requires dye -- you'll need to harvest rank 4 spots to get dye moss, and you'll need pretty beefy alchemy to make the dye, but you might be able to buy your dye with cheap ffxiv gil and still make a profit, depending on how the economy develops.
So botany + weaving is the perfect combo in FFXIV. If you choose this, I am sure you will have a good harvest.