Here's my embark profile, spoilered for length-
[PROFILE]
[TITLE:FEWTREES]
[SKILL:1:MINING:5]
[SKILL:2:MINING:5]
[SKILL:3:MINING:5]
[SKILL:4:FORGE_WEAPON:5]
[SKILL:4:FORGE_ARMOR:5]
[SKILL:5:PLANT:5]
[SKILL:5:MECHANICS:5]
[SKILL:6:BREWING:5]
[SKILL:6:PLANT:5]
[SKILL:7:CARPENTRY:5]
[SKILL:7:MASONRY:5]
[ITEM:3:WEAPON:ITEM_WEAPON_PICK:INORGANIC:COPPER]
[ITEM:1:WEAPON:ITEM_WEAPON_AXE_BATTLE:INORGANIC:COPPER]
[ITEM:1:ANVIL:NONE:INORGANIC:IRON]
[ITEM:1:SEEDS:NONE:PLANT_MAT:BUSH_QUARRY:SEED]
[ITEM:5:SEEDS:NONE:PLANT_MAT:POD_SWEET:SEED]
[ITEM:5:SEEDS:NONE:PLANT_MAT:MUSHROOM_CUP_DIMPLE:SEED]
[ITEM:5:SEEDS:NONE:PLANT_MAT:MUSHROOM_HELMET_PLUMP:SEED]
[ITEM:5:SEEDS:NONE:PLANT_MAT:GRASS_WHEAT_CAVE:SEED]
[ITEM:5:SEEDS:NONE:PLANT_MAT:GRASS_TAIL_PIG:SEED]
[ITEM:30:DRINK:NONE:PLANT_MAT:POD_SWEET:DRINK]
[ITEM:30:DRINK:NONE:PLANT_MAT:MUSHROOM_HELMET_PLUMP:DRINK]
[ITEM:30:DRINK:NONE:PLANT_MAT:GRASS_WHEAT_CAVE:DRINK]
[ITEM:30:DRINK:NONE:PLANT_MAT:GRASS_TAIL_PIG:DRINK]
[ITEM:120:MEAT:NONE:CREATURE_MAT:ANT:BRAIN]
[ITEM:9:WOOD:NONE:PLANT_MAT:TOWER_CAP:WOOD]
[PET:1:DOG:FEMALE:STANDARD]
[PET:1:DOG:MALE:STANDARD]
[PET:1:CAT:FEMALE:STANDARD]
[PET:1:CAT:MALE:STANDARD]
It's not optimal by any means, but it hasn't yet killed me. I generally dig a modestly sized spiral entryway on the first sand level under the wagon, culminating in the start of the aforementioned 3x3 spiral staircase located directly underneath; the flat entry spiral ends up being trapped and systematically rebuilt with fortifications until the traps can be supplemented with ballistae. I dig down until I hit semi-molten rock (i don't know if it's just me, but the magma sea never quite extends to the corners of the tiles so a 4x4 embark puts you, at the center of the map, over a pillar of rock right down to the semi-molten), start digging exploratory tunnels until I hit a flat patch of magma, and structure my fort from there up. Of course, if you start on an (odd)x(odd) embark or otherwise hit magma, the basic principle is the same but you save exploratory tunneling. You can generally trade for enough wood and food for the first few years if you have both dwarves and elves trading with you, which is more than long enough to divert any water in the caverns down to make the central waterfall (you have to rebuild the staircases around that level to make room), ideally stopping it with lever-controlled hatchways on the farm levels. I'm lazy like that.
You're right in that farming is an early priority, but there's nothing wrong with doing that and starting metalsmithing simultaneously; it's why I build my forts right on top of the magma, anyway. I've also considered dropping that central sand tile at the start of the central staircase down to make a ridiculously convenient glass industry as its way has been channeled out anyway, as long as it's dropped below the waterfall's water recovery level before the waterfall starts.
The only thing you really have to watch out for is nasty things coming through the caverns; if you're worried, you can cave in sheaths around the staircase rather than building them, assuming you make the rock layers between caverns thick enough.
That's how I do it anyway.