We have exact same car, at least my daughter does and I work on it.
1. Yes depends on the life and the driver. Bad driver could have damaged the clutch or caused it to wear prematurely. Not checking & topping up oil regularly can run the engine low and damage it. If its been used in country, driving highways that is way better. Short trips and stop start traffic can be hard service for drive train ie motor, clutch, brakes. Regular trips to beach areas with salt spray and not at least rinsing the car after can cause early rust. Use a sun visor to protect dash and garage it whenever possible. When its washed hose out under guards to remove mud.
2. Exhaust note will sound different when you sit in back compared to front and nothing like what you hear on the street. Original mufflers usually last longer than after market replacements so leave it alone if nothings wrong with it.
3. Our car has 150k on it. First thing I did to it was adjust the clutch pedal as it was engaging too close to the floor. If the floor mat got under the pedal you couldn't change gears unless it was moving. Its not normal to be spinning the wheels. You are "dumping" the clutch given you are new to car ownership, common for newer drivers. A little less throttle and a little more slip with the clutch will give you a smooth movement from stopped. The clutch usage to get the car moving from stopped needs to be a little more careful than when its moving and your going thru gears, your probably using same technique for both. Driving is all about being smooth and your car will appreciate it. It just takes practice and time. If you keep doing it you are likely to run into back of someone who moves then props, wear out your tyres early, break a driveshaft, burnout a clutch or break springs in the clutch.
4. Changing gears is usually easier when the engine/gearbox is at operating temperature as the lubricants are thinner. This could also be affected by the clutch pedal adjustment or floor mats under the pedal. If you put the car in gear with foot on brake and clutch hard to floor, then gently and slowly raise clutch a little while watching the tachometer, you will see the revs drop as it engages. If this happens straight away then its too close to the floor like mine was. You should be able to lift it 15mm or so before it starts to engage. When clutch engages too close to floor gear changing is difficult particularly when the car is not moving. Also again as you are new driver try to relax arm/hand grip on gearshift and guide it to where it needs to go rather than shoving it there. It should just need pressure in the general direction with an open but cupped hand and not a death grip on the stick. This allows the stick to find its own path to where it should be even if the shift linkages are a bit out (I would doubt linkages are out if its only got 100k on it).
5. Well I wouldn't worry about the squeek in the clutch unless you can identify exactly where the noise is coming from. Like pedals, hydraulics or under the bonnet. Clutches can be tricky to work with, adjusting pedal on that car is not easy (remember I've done it). If the pedals squeeking don't bother spraying wd40 or anything around there as all you will do is get it on the pedal rubbers (bad) and it wont get into where its needed. Might need a bit of grease in the pedal pivot requiring pedal removal but I suspect its the hydraulics making the noise.
6. Idle speed is usually factory set by an air valve/vacuum sensor and the computer. If its not stalling don't worry about it. They do usually idle better after oil change. Also if your clutch pedal is too low and causing a slight engagement obviously the idle speed will drop. Make sure its in neutral and warmed up with a/c and headlights on and if it can idle like that its fine.
7. Yes the car is very zippy. It has a high power to weight ratio mainly due to it being a small car. Like I said try and drive smooth. The way you describe doesn't sound like you are. Smoother you drive the less accelerator you need, less brakes you need, less fuel used, less brake wear, less gear shifts, less maintenance and you will probably get where your going just as quick or close enough to it, in a much calmer and safer state.
Hey just curious do you have trouble working out which car is yours in a carpark? Ours also silver and I guarantee everywhere we park there's at least 3 or 4 others within sight.