hello,
first off welcome to the forum, i don't know if this will help you much but its just my 2 cents
Mechanical work: limited mechanical knowledge is needed (i was 12 when i did my first and sadly only build in 2012 (had to sell my earlier this year due to law being changed.) but however a little research on Google and this forum wouldn't hurt.
upgrading is tricky Sometimes, however this forum will always have the solutions.
Maintenance: comes down on what kind of quality kit you have. If you don't mind paying for a good kit, go for it. Simply use good (one of the best) quality oil and petrol and you tighten bolts regularly you shouldn't have a problem. buy a cheap kit.... your in for it. i bought a cheap kit and it took me 1.5 years to get it to reliable state that i could go for a ride and not have to bring a basic tool kit with me though at 12 you could imagine money is tight so that played a
small part of it.
things to do when you get the kit don't use the spark plug they include it is SH$T. it played havik on my bike. i got three of those dud spark plugs and i threw all of them out the window.
Get a NGK BH56 or something like that. get some rubber to use on all the mounts to put in between the mount and the bike frame. this makes it stop half of the vibration and keeps the bolts tighter for longer.
lastly what country and state are you located in the laws can vary.
you can wait around for Fabian and jaguar and a few others to tell you more they are legends on this forum and helped me out countless number of times.
The brake in period is during the first 500kms of the engines life. you need to keep from going over 25kmh and riding 30 minutes or under at a time. some say its better to full ball the engine however ill leave that for Fabian to answer
these are two stroke engines so they require the fuel and the oil to be mixed together. i had a fuel container that held 5L of petrol so i had to put 300ml of 2 stroke oil with it. (the ratio is 16:1) this changes after the
break in period is finished and goes to 20:1
the reason for this is so the piston rings can seed and create a perfect seal for compression.
Hope all of this helps.
-Bazz