D&D Nerdery - Questions

As mentioned in the previous post, I went to the local game store to participate in the Game Day Event for Dungeons and Dragons. I walked out with some minis, a giant reusable battle grid, and a set of dice (I "won" a scenario which netted me the dice). I also walked out with some questions - questions I did not have the foresight to write down and my still-functioning-on-little-sleep-and-complicated-with-moving-slash-buying-house-details cannot completely recall.

I spent some time flipping through some of the Core set today as well as reading some of the DM Guide for the Keep adventure. My reading answered some questions and presented more. There are currently 3 that stand out in my mind.

1. Healing Skill - I think I understand now that one use of healing skill is First Aid. I assume that First Aid applies some kind of healing to an adjacent ally. How does this work? Does it use the other players healing surge if the check is successful? Or is there a die roll to determine the number of hit points added to the hurt ally? If so, which die? I assume this can be done while in combat as a standard action? Is there a limit to the number of times assuming the person succeeds in the check? Also, how is the DC for a healing skill determined?
2. Perception Check - This is a question specifically regarding the Keep adventure (potential spoiler). The kolbolds ambush the players at some point in the adventure. The DM Guide calls for you to ask the players to make a Perception Check with a DC of 25. I understand that you want the DC to be hard and 25 counts as hard but I'm looking at the premade characters and unless I just do not understand how the perception check works, it seems only 1 can possibly pass the check and that is only with a roll of 20. My understanding of the perception check is that the players have to meet or beat the DC. So, in this case, they would have to make a 25 or better by rolling a d20 and adding their perception modifier. One character in the premade characters has a perception check bonus of +5. If he rolled perfect, he would not be surprised but no one else in the party stands a chance. Am I missing something? Am I misinterpreting something? I agree it should be hard (otherwise there is no point in an ambush) but this seems just about impossible (for 4 premade PC people it is impossible).
3. Fortitude, Will and Reflex Defense - I understand that say an enemy makes a magic attack against a PC that instead of AC it might attack reflex. The enemy has to roll the d20 higher than the reflex defense figure of the PC it is trying to attack. Maybe this was a table rule specific to this particular DM (like the critical failures where I kept hitting myself in the damned head) but there were many times when I was asked to roll a d20. Supposing my Fortitude Defense was 12, I had to roll under 12 in order to be saved from damage. There was once I rolled in order to determine whether I took full or half damage. Is this a save roll? If it is a save roll am I mistaken in thinking that by 4e rules you just have to roll better than a 10 to be saved? My interpretation of the rules thus far have made it seem that the defense figures appear to be different versions of AC for different attacks and the save roll seems to be unrelated to the defense in this edition.

I'm going to make an attempt to write down other questions that come up as I continue to study the information. I am not sure whether to be giddy with excitement or sick about the fact supplements with more confusion will steadily be released just as I get a grip on the basics. 4e is decidedly simpler than the previous edition but there is still a lot of information to be processed and figured in - feats, powers, racial and class modifiers, line of sight and line of effect, triggering actions, attacks of opportunity, flanking, and on and on it sometimes seems.

I guess along with my goodies both bought and given I also took home the realization that it is not necessarily an exact science. One DM was pretty straight forward. The next guy used critical failures which sometimes resulted in an enemy bumbling his attack and inadvertently killing one of his own skeleton warriors. The exploding skeletal bodies created shrapnel which hit PCs (I believe this may have been one of those roll to see if you take full or half damage deals). It certainly made it interesting and I guess as long as the players go for it, the DM can be creative like that on the fly.