1. Tokyo Marui. Pretty much the inventors of modern Airsoft weaponry. Most Airsoft rifles and Pistols are based or copied on them. For AEGs, that mean that most parts will be compatible with your rifle is said rifle is "TM" compatible.
2. Longest is variable. What I've read around is that except for particular setups, you should not need above 500mm. The rest is wasted and could affect negatively your accuracy.
3. The version of the gearbox, as the name suggest, is the generation of gearbox produced. That does not mean that a v2 gearbox is obsolete, but the v3 was developped to overcome some of the previous version's problem. One big difference between the v2 and v3 gearbox is the motor attachment. In the v3 box, the motor is attached to the gearbox, and in the v2, the motor is held by the grip itself. Another difference is the wiring being outside in the v3, allowing easier wire changes.
For other boxes, like v6 and v7, I don't know much about it, but they are basically the same thing as the others, used in rifles where the standard boxes could not be fit, for example the m14 and the p90.
4. High speed means that the motor will turn FAST. That means that a very high rate of fire can be achieved with them. High torque means that it will be STRONG, meaning the first shot that needs to overcome the spring before the movement is started will be faster.
The difference between the two is that the TORQUE one will shoot faster for the fist shot, but will not have a higher rate of fire compared to the SPEED one. The SPEED one will turn faster over time, but will not be strong enough to compete with the TORQUE one at acceleration and first shot quickness.
Others are either High SPEED/ High TORQUE hybrids, or weaker motors that do neither.
5. They are easy to get in Canada, but the forum's policy is that we will not disclose such information until you provide proof that you are 18+. For this, we have an Age Verification system, which you can learn about in the FAQ section if the forum.
6. Recommended order depends on your needs, but people around here and I will suggest you that you do NOT upgrade the rifle until it breaks. That sounds silly but it will save you a lot of trouble. The recommended actions are to open the gearbox to clean the inside, re-shim the inside and re-grease it properly, then leave it like that. You could also change the hop-up rubber, but this might not be needed with our setup and could cause more harm than good. I know this answer sucks, as I was eager to upgrade my rifle too, but it's for the best that you use your rifle before dumping money and possibly create more problems.
7. Welcome to AirsoftCanada. Do not be afraid to ask questions, and if you follow our simple rules, you'll see that it's a great community around here.
Like mentioned below, all this stuff can be learnt from reading, but I hope I got your curiosity and gave you the will to read more and more. It becomes simple after a while
I'd suggest you to fill your profile information, such as your city, so that people can help you and target your
Have a nice day.