New Commuter

Don't know if I count as a commuter, only do 1.5 miles to uni (but there and back twice a day) but I have a few questions and tried to search the answers but didn't really find what I was looking for, and hoped some of you could help 
First of all, i have a 2008 Scott Sportster P6, and its by far the best bike I have ever had (previous being some cheapish barracuda full sus when i was 14 and some Apollo rubbish before that)
1) On helmets whats the point of the plastic 'fin' on the front that unclips? I think it just makes the helmet look cooler, but does it serve a purpose?
2) On my bike, there is an annoying tick/grind feeling when pealing, but not when free wheeling, whats this likely to be?
3)When changing down gears with the quick shift thing, some times I press the lever in, but it doesn't quite down shift, and I have to give it another nudge. Am I just not pushing far enough, or has something stretched (baring in mind Evans should have sorted this last week with the first free service)
4) How easy is it to make your wheel untrue? Im sure the front is by about 2 mm somehow, and think it maybe due to potholes on the way to university, but not sure if that's possible?
5) Mudguards, shall I get some? Not had to cycle in the rain yet, so don't know how much spray I will get, but should I get some like the crud ones for £15 that look quite slim?
Thanks for any help, and sorry if the questions are stupid, I'm really new to bikes and hopefully one day want to fix problems myself without having to go to a bike shop

First of all, i have a 2008 Scott Sportster P6, and its by far the best bike I have ever had (previous being some cheapish barracuda full sus when i was 14 and some Apollo rubbish before that)
1) On helmets whats the point of the plastic 'fin' on the front that unclips? I think it just makes the helmet look cooler, but does it serve a purpose?
2) On my bike, there is an annoying tick/grind feeling when pealing, but not when free wheeling, whats this likely to be?
3)When changing down gears with the quick shift thing, some times I press the lever in, but it doesn't quite down shift, and I have to give it another nudge. Am I just not pushing far enough, or has something stretched (baring in mind Evans should have sorted this last week with the first free service)
4) How easy is it to make your wheel untrue? Im sure the front is by about 2 mm somehow, and think it maybe due to potholes on the way to university, but not sure if that's possible?
5) Mudguards, shall I get some? Not had to cycle in the rain yet, so don't know how much spray I will get, but should I get some like the crud ones for £15 that look quite slim?
Thanks for any help, and sorry if the questions are stupid, I'm really new to bikes and hopefully one day want to fix problems myself without having to go to a bike shop

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1: The peak is there to look cool and to try and keep rain out of your face, as I understand. It has nothing to do with crash-worthiness.
3: Readjusting your derailleurs should sort that. Assuming that it's the rear one, this tutorial should show you where to look. You'll probably just need to follow the cable adjustment bit.
2 & 3 are probably related, as per the previous fella (don't think I can type that name and get it right) getting the gear shifting adjusted correctly should be a good satarting point to sort it out.
4 - fairly easy!
5 - get mudguards if you are commuting every day - they make a big difference.
Hope this helps!
Oh, and have a look at your brakes as they're very easy to adjust if they're not properly in line. Truing a wheel isn't hard (potholes can indeed cause this, you're right) as such but it's trickier than most and I probably wouldn't try it at your level of experience. A couple of millimeters is probably fine to ride, but if it gets worse it's worth taking to the shop - they should be able to adjust it very quickly for a minimal sum (or free).
Blog (incl. bikes)
I understand it's to keep the sun/rain out of your eyes. It will not protect your face in a crash - it would just snap off.
Is your chain dirty or not oiled? That would be the first place I'd look.
Can be pretty easy depending on your weight and the quality of wheel. See Jamey's things that go wrong with my bike thread!
Depending on what you cycle in and how much you like doing laundry, mudguards might well be a good idea!
Viner Maxima, Tifosi CK7, Giant Bowery, Old commuter.
I think it comes when I push down on the left pedal, so must be something on that side, how to I find out what it can be?
Its when I change down the back cogs say from 6 -> 5 especially that the gears get stuck, so will have a go at the tutorial posted
Be careful: pushing the left side down also pushes the right side up.