I'll answer to the ones I have any kind of experience with....
1. I do it and so far, no bad experiences. (edit) I don't squeeze the bag 'dry'. Just some to get a little more of the liquid out of it. Once it drips when I put pressure on it, I'm done (edit) If the bag tears while squeezing it, I'm guessing it would cause 'issues'
2. So far, never heard of anyone doing this. I've learned not to try and re-invent the wheel, especially early on in your experience. On the other hand, if you are making partial boil batches, I don't see why (as long as the water is boiled/purified) why it wouldn't hurt.
4. Don't time your bubbles. Bad Habit. Wait about 18 days and check the gravity. Check it again on about day 21. If they are the same, you are good to go. These are generalizations on the number of days (about 3 weeks). Either way, wait until your gravity (or where it falls on your color chart (I'm not framiliar with your particular hydrometer)) stays stable for a couple days.
5. Partial mash is using more grains and less extract. Times and temperatures for dealing with the grains become more critical. Overall, not a huge deal though. Some techniques change, but it really isn't all that difficult of a switch. Same for moving on to All Grain. Partial Mash is kind of the middle step between Extract and All Grain. The more towards All Grain you go, the more complicated it gets, but you also gain more control. Think, making your own Spaghetti Sauce v.s. Using Sauce out of a jar.