When your declare your First Strike Deathtouch creature as a blocker for multiple attackers, you must choose the order in which your blocker will deal damage to those creatures (the owner of a creature chooses the order it's damage is dealt to creatures it attacks or blocks). When this is done, and play progresses to the combat damage step (for creatures with first strike), you must then assign lethal damage to each creature in the order you chose earlier. The addition of deathtouch means that lethal damage is 1 damage for any creature, including indestructible and regenerated creatures. This means with a 2/2 first strike deathtouch creature, you can assign lethal damage to the first 2 creatures in the order you declared.
When all creatures have no more damage to assign, the damage step ends, any creatures assigned lethal damage die and combat progresses. As you would expect any remaining creatures then deal damage to your creature as normal. In your example, you would kill the first 2 3/3s and then the rest would survive to kill your 2/2.
in the second scenario, the result is very similar, all creatures that can, must block your first strike deathtouch creature. Next, you choose the order of those blockers (just as before, the controller of each creature declares the order in which it's damage is dealt), and when the damage step comes assign lethal damage in that order, killing 2 of the 5/5s and leaving 3 standing to then finish your creature.
Deathtouch makes any damage assigned lethal damage, however just as a 0/4 creature with curiosity deals no damage to a player and hence its controller does not draw a card, so too a creature with deathtouch assigning 0 damage to a creature cannot destroy that creature.
If your opponent has 1,000,000 attackers (e.g. through Splinter Twin and Deceiver Exarch combo), and you wish to survive and kill all those creatures, I encourage you to look at Engulfing Slagwurm which has a kind of "Super Deathtouch" which just kills any creature that blocks or becomes blocked by it, giving you life equal to those creatures toughness. In the example I just gave, you would not only survive but stand to gain 4,000,000 life in the process.