[QUOTE
1- do floggers really cause pain or a discomfort?
2- which are easiest to start with? (which is controlled best?)
3- Are they all legal?
4- do the lengths differ only in control or is bigger better?
5- how are they rated from most pain to least pain?
QUOTE]

1- Yes, they really can. There are a few ways to use a flogger, techniques, I guess. 1 is to twirl the ends quickly and just have the tips of the straps make contact, which stings a lot, but isn't a 'deep' pain. Or you can just drop the straps on the submissive, without following through. Some people call that a massage flogging because it's not painful. If you follow through, that brings deep pain, especialy with a heavy leather strap flogger.
2. I think a crop is easiest, it's whippy so very responsive, but as was stated, you can definitly get enough into it to get your point across, just start off easy until you learn yours.
3. Umm...I thought so, local laws might be different somehow though
4. Bigger isn't necessarily better, the longer it is, the harder it is to control exactly where it lands.
5. That one you'd have to ask a sub, but I'd say a wooded paddle could be near the top of the list too.

Good luck, and just try things out and start slow.