For future reference, you wanna refer to this thread if you want questions answered:
http://smashboards.com/threads/offi...e-a-quick-question-ask-it-here.201103/page-52
1. Pit excels at keeping his opponent at mid to far away or above him. His uair, arrows, jab, and aerials all kinda push people out to set up for arrow harassment and the like. What makes Sonic effective vs. Pit is that he's able to get into his defensive bubble pretty easily, and can spin under arrows that aren't curved to strike Sonic on the ground. Once Pit's off the ground, or if Sonic gets into his zoning, Sonic doesn't have a hard time adding damage or just punishing Pit's options. Pit also doesn't live super long, so Sonic's problems with KOing aren't incredibly apparent here.
2. Videos with X, D1AOS, and myself would probably be best, but we don't really have much recent content. You can find most videos of us in the Sonic video archive in the main subforum here. For doubles, I recommend True Blue. He's honestly probably the best Sonic at doubles anyways.
3. There's not many Sonic techs outside of spin cancels. You have the spinshot and the iSDR, as well as auto-cancel dair, but there's not much to him as far as that goes. It's mostly just execution and spacing of the cancels and whatnot, and how to manipulate them to force your opponent to use punishable options.
4. This question's kinda hard to answer because it's directly based on the character you're fighting. Using it on Olimar is kinda risky because of how many options Olimar has that beat it, whereas using it on Donkey Kong is heavily encouraged because of his lack of options against it. In general, you shouldn't be using it from super long distances as a means of attacking since it's incredibly easy to read. From far away, it's better off used as a way to close the gaps between you and an opponent (since it's slightly faster than dash I believe, but only at full charge), or as a follow up for some aerials. DownB is catered more towards aggressive plays since it's easier to follow up with, while sideB is mostly defensive due to the invincibility on the initial hop you get out of it, though both can be used for either once you understand your options.
One example would be using downB defensively by full hop retreating with it, or tilting diagonally to slightly alter your landing during the spin. SideB's invincibility can be used to parry and immediately counter an opponents option, and it's a great offensive tool for eating through ranged characters or projectiles.
5. Sonic's only practical options are uair for vertical, then bair, dsmash, and fsmash fresh. If you're having trouble KOing, it'll mostly be because you're using bair too much for damage racking and not enough for KOs. It's easily our best move to land when it comes to knock outs, so try to find other means of adding up damage besides the bair. Grabs are usually my go-to option for adding up quick percents and dropping the stale counter on my KO moves, so you can try that out if you want. Above that, grabs are really good for setting up land sharking, and edge guarding.
6. Don't use nair for momentum cancel. Fair is a bit faster, then uair, but you should always be using fair. Afterward, either downB or sideB (depends on how good your timing is on downB releases). DownB and SideB are essentially bucket brakes, and cancel all backward/upward momentum from knockback, so they're always the best option. Fair > DownB is the best Sonic has, but if you're having trouble with DownB's release, SideB is your best bet. The difference between them IS there, but it's kinda negligible for the most part. The only problem is that sideB DOES suck you backward a bit during the hop.
7. DACUS is okay as a once-per-set kinda deal, but you put yourself at a huge risk if you miss. You normally don't want to risk cheesing it unless the enemy keeps trying to trade with you during it's use. Usmash has a few frames of invincibility on the transition between the ground and the air, so it's good to try and bait attacks and countering with it, but that's about it. DACUS can also spike enemies if you're lucky.
8. He can, but the distance he get is so negligible to DACUS that it really isn't important at all.
9. Sonic's priority is fine. He just doesn't have range on a lot of his moves.