As for the orcs, best defense is a good offense. You'll have extra labor, I've done these embarks before, either you keep them tasked on mindless things (gathering after farms are set up) or you let them idle. Rotate your hunters and use the bones and leather they bring in to make armor and train marksdwarves. You might be able to survive early orc sieges with a good marksdwarf squad. That's really your only hope though, as you can't make a barracks without a fourth item, so any melee training is out of the question.
I've never played with orcs but this is how I handle aggressively dangerous terrain for 0-point embark:
1) No rivers.
2) On embark find a good, safe watering hole. Deconstruct wagon and use a wood stockpile and meeting zone to order all dwarves and logs to the encampment.
3) Forget farms, harvest some berries and whatnot for instant food, but get two of your seven on fishing.
4) Make refuse piles, build fish cleaner, butcher, tanner - job up.
5) Slaughter pack animals.
6) Butcher -> Kitchen (Cook tallow, then roast meat and tallow together, add berries and seeds to taste.)
7) Tanner -> Leatherworker (Make armor, leggings)
Kitchen -> Bowyer (Make bone crossbow from one set of bones - control for fishbones if you have them by this point.)
9) Leatherworks -> Crafts shop (MAke bone bolts from remaining bone stacks, but don't use fishbones for this, no point.)
10) Hunt.
11) Rinse and repeat cycle.
11a) Use fishbones for more crossbows or bone armor pieces.
This requires an insane amount of micro but you have only 7 dwarves and no mining to plan so what else are you going to do?
When the orcs show up? Spam them with bone bolts. When you drop a squad, grab their weapons and arm anyone who's left.
12) Pray.