Miscellaneous Questions
1 errateaed to +- 60 iirc
With regard to 2, the effects can be described in a different fashion with the same result. The leg blown off situation you described (pretty nasty at 8 critical wounds, with a chance of death too!) could be represented differently. "As the needle drives past your armor into your skin, you feel a quick rush and a burning sensation. The toxins coursin through your body cause the arteries in your leg to burst, rupturing your leg and leaving only a bloody stump in its place."
With 3, there is no new critical 'roll'. You just add the new damage to the previous. So if you had 2 points of critical damage, then take another 3 points of damage (after armour and toughness bonus soak), you would be at 5 points of critical damage. The effects are cumulative regardless of where the hit lands. The book has a concise example on page 201.
WIth 4 (labeled 3 again, regarding fate points), awarded fate points are permanent. That said, the GM has ultimate decision on fate point refresh and allocation. So you might not always recover fate points at the beginning of a session. (In games I play in, fate points are typically refreshed between missions, which can span a session or few.)
On your last point, anyone with the medicae skill can attempt to test that skill for first aid. Damage recovered varies based on how heavily damaged the person receiving care is. On success, lightly wounded heal the Int bonus of the person performing the test, heavy and critical recover 1 wound. Failing by by 3 or more degrees, though, can cause damage or death (page 104 of the book for the skill).
A stimm (drug) can also be used to temporarily ignore effects to characteristics from damage or critical damage.