NWCtim

You get a set amount (half or half+1 of the number of different cards in that set) randomly while playing. Once you reach that number you can only complete the set via trading/buying or by getting random booster packs. The booster packs are incredibly rare, with your chances of getting one increasing with your Steam level. I've gotten 2 or maybe 3 boosters since I signed up for the STC during its beta, and none of them have been recent. You also have no control over which game the booster pack cards are for, except that they are always for a game you own.

Just the most recent one. The only reports you can store results from multiple sites are EVA and Collected Sample reports, and then only one per site. If you want to recover (instead of transmit) multiple goo container experiments in a single flight, you have to have multiple goo containers on your ship. Also, while transmitting results does mean you get less science from that individual experiment, the value of the next experiment you run won't be diminished as much. So if the first goo experiment is worth 10 points and recovering the experiment causes the second one to be worth 5, then transmitting the results would caused the second one to be worth 8 instead.

Your command module can only hold 1 crew report at a time, so the best thing to do is transmit it, especially since you still get full value from it when transmitted, unlike almost every other experiment. (Don't worry, you just have to run the experiment more times if you transmit the results rather than recover the experiment). And yes, you need an antenna to transmit data, also antennas require electricity to transmit data.

16 transmits at half the speed of the 88-88. It also uses less power per transmission cycle. So if the 16 takes 10 seconds and 50 electricity to transmit the results from an experiment, the 88-88 will take 5 seconds and 100 electricity to transmit the same data. On the other hand, if you have two sets of results to transmit at the same time, then two 16s will take 10 seconds and 100 electricity to transmit both sets simultaneously, while the 88-88 will take 10 seconds and 200 electricity to transmit each set one at a time. Something to bear in mind if you like to run multiple experiments at once and electricity load is a concern.

As long as you are somewhere on the surface of Kerbin, your craft can be recovered.

The 'higher end' antennas consume more power per transmission cycle and they cycle faster, allowing for a faster transmission rate. Alternatively, having multiple antennas means you can have multiple data streams transmitting at once. Assuming my understanding of how they work is correct, having two Comm 16s gives you the same transmission rate as a single Comm 88-88, while consuming half the power. Obviously, the parts aren't really balanced at this point. As far as science loss goes, there is no difference. Fortunately science degrades at a zero-sum rate, even though transmitting the data causes you to only get a fraction of the science results, the value of the next time you run the experiment only degrades by that same fraction of normal. In the end, the only thing you lose by transmitting it is the time and electricity it takes to transmit the results multiple times.