The reality of this situation is that your basic info is already out there; it's in so many databases you have absolutely no control over that it's not even funny. Many of these databases will have a security breach eventually (if they haven't already), so it really doesn't do you any good to try and keep your basic info to yourself.
If you don't feel comfortable completing an offer or signing up for a freebie then simply skip that one! You always choose when and what information you want to share. Besides, the worst that could happen is you sign up for a fake freebie and get some check fraud scam in the mail, or something stupid like that. On the very rare occasion that's happened, I've actually had a good laugh, because the fraudsters paid for the postage, and most of them are paying to send from outside the country, so it's certainly not cheap. You really have nothing to lose, and everything to gain!
The things you should probably only give to P2S are your primary email address, and your home and/or cell number(s). It's easy to create a free alternate email address for doing offers/freebies, so that way your primary doesn't get spammed. The best thing to do about unwanted/untimely phone calls is to get a free local number from Google Voice, which will give you total call control! Check out the ECP P2S Tutorial for more tips.
The only other things worth mentioning are that you should never give out your Social Security Number (SSN) without being absolutely sure it's a legitimate business you trust, and you should be careful not to use the same password for offers/freebies that you use on important accounts. That's really all there is to it!
How much you earn mostly depends on your demographic, the types of offers you complete, and the time and effort you're willing to put into it.
In my experience so far (being in the US), it's trivial to earn $1-5 USD a day with a little bit of time spent doing just the free offers/daily surveys! If you're motivated and have the time I've seen people earning $25-50 USD a day just doing the recurring tasks (when the right ones are available)! There are lots of ways to earn, and they're always adding more, so just play around and figure out what you like to do that works for you.
This may not seem like much, but it adds up pretty quick. This is not even counting referral bonuses or winnings from games! Plus with the daily surveys, you have the added benefit that your input actually helps improve and create products and services!
The best way is to use a VM (Virtual Machine) such as VirtualBox or VMware. This will allow you to run a completely self-contained installation of Windows in which you can safely run untrusted software. Once the offer approves and you've paid things forward a bit, you can simply revert the VM to your snapshot, knowing that everything is now exactly as it was!
The alternative is to use a sandbox environment such as Sandboxie, which is theoretically a little bit less secure, but doesn't require as much hard drive space. Some people find sandbox environments confusing and some installation offers may not work properly in them. If you don't feel comfortable doing these sorts of things you can always skip/ignore the download/install offers, but it's really not difficult. It's a great way to earn some extra cash or points!