Andrew R Stewart 

1- Wheel servicing should start from the center. This is the axle and it's fitting within the bearings. No slop and free spinning. Only then can the rim be looked at with assurance of only the rim issues being present. Like is the rim off center (out of dish) or is it not true (either side to side or radially). Once the wheel is determined to be in good shape then how it's secured and located in the drop outs is next. A good wheel can look off center if the axle is not fully up in the drop out slots or be sloppy loose if the axle nuts/QR skewer is not tightened fully. If all these possibilities are good then the fork's alignment or headset adjustment needs attention. Without a solid foundation as to how to go through the logic steps or the skills to fix those that are wrong it might be faster and easier to let a shop handle things. But these abilities are not hard to learn, just that for some the learning process has more road blocks then others.

2- Unless the bike is being ridden on soft and deformable surfaces the tread directions have VERY little effect. It's not like a car with a need to vent off water. If the bike does see soft surface use AND if the tires don't have a directional arrow then just try the tires each way and make up your mind.

3- Yes, the wheel first needs to be centered within the fork. Then the brake arms, the pad position on the arms and the arm springs all need to be first set as symmetrically as possible, side to side. From this base line pad position on the arms or spring tensions can be played with. The cross 9straddle) cable also usually needs to be symmetrical in it's lengths from the center cable connection to each arm. The arms need to pivot freely on their posts with neither binding more then the other.

4- The left crank arm likely has a tapered square hole that fits on to a matching tapered square axle end. When the tow tapers don't perfectly mate the arm will never stay tight. The axle is usually made of a hardened steel. The arm usually a softer material. if the arm is allowed to come loose just once and then ridden this way the hard axle will wallow out the arm's tapered hole. Now the two won't fit well together and the arm will always come loose. The repair is to replace the arm with an undamaged one and after initial rides re torque it's retaining bolt. this will cause the arm to draw up on the taper a bit more compensating for the slight molding the arm's hole goes through with the first use. Sometimes a second re tightening is needed a few more rides later. The arm should be mounted on a dry and clean axle, the retaining bolt's threads greased.

There are many on line guides for these issues. Andy.