[1]:
-Friends. GW can help out here if you have none
[2]:
-Mics/Speakers. Ebay + $5 = solved.
[3]:
-Time to spend 1-2+hr sessions. It takes trial and error to get everyone onto the same team, then squad, because BF3 doesn't like self-managements of squads. Once you DO organise yourselves into the same squad though, BF3 will make sure you spawn into the same team/squad every round afterwards. That's why you'll need to be prepared to invest some time into getting everything to work right - then enjoy the game for even longer to get your investment back.
[4]:
-The patience/mindset to get your first few unlocks so you're no longer cannon-fodder. Modern Warfare's been better at this. The starting guns in MW2 are powerful enough for you go dive into the action without sucking too much. The latter weapons add to the fun without necessarily increasing your lethality. In BF3, levelling up is required to get some better guns and gadgets. You must weather the storm before getting to those. To make the process slower, the US and RU start with different guns, so you must get xp for those separately to unlock their scopes etc.
[5]: You will find that a fair chunk of time will be spent travelling on the map or trying to spot enemies to shoot. If you can't handle that and need to shoot people quickly (think Quake), then this game may not be for you. General online game-play isn't
that tactically demanding, but for the most part, run-and-gun won't work. (A bit hypocritical for me to say this, but anyway..
)
[6]: I would suggest to start off playing a bit of Team Death Matches in the beginning. It helps you get used to the new guns, makes it easier to learn some of the maps and enemy density helps you get more kills.
[7]: I haven't touched SP or co-op so I can't tell you anything about that.