Tinker is both an extremely mobile ganker (BoT and dagger and hex) and also an extremely effective pusher. The thing is to do well in early game. As the post above me says, Tinker is like Nevermore in the sense that he will either bring your team to win or feed like a retarded goblin.
1. You should max laser first over rocket, as it is pure damage while rocket is magical.
2. Yes, getting BoT is your main priority, as it gives you much more freedom and
shitloads of mobility. However, if u feel that ganking early = easy kill then go for it.
3. ALWAYS BoT before soul ring because getting BoT first means your soulring should come within a few minutes after, but not vice versa.
4. If there is a gay Lion on the other team, or someone of the equal gay rank, get hex first and hex rearm hex rearm etc that fag. Other wise you can still rush hex or get shivas for better pushing and survivability. Or get dagger > dagon for ganking
5. Both. If you get dagon dagger you can gank extremely effectively as they cant run away from you.
6. its about the width of your screen, play more and you get used to it.
Read this extremely concise but awesome guide on tinker: