I think you're thinking a little too hard about this, but better to be safe...
1. I don't fully understand what you're asking here. Are you asking if you should try and extract the methylphenidate first versus just crushing the pill and snorting it? If so it's really personal preference, but most people just snort the whole damn thing almost regardless of what pill they're using, if it's possible to insufflate in the first place. It's a little gross and gunky but not a huge issue if you're not using regularly. If this is not what you're asking please clarify. Don't swallow anymore than you have to. This defeats the point.
2. Personally I wouldn't blow my nose for a while after snorting something. You want it to "sit in your nose" for as long as possible so it all has time to get absorbed. A drop or two of purified water dripped into your nose from your (clean) fingertip can help some with this, or a spray or two of saline solution before and after snorting. If your nose is running, by all means wipe it gently.
3. Sort of covered above, try not to blow your nose. It can definitely affect how much is absorbed, because if you blow your nose too soon and blow out a bunch of drugs that your body hasn't absorbed yet... well, do I have to continue? It's just better not to, because while 15-20 minutes should be about sufficient why would you want to risk ejecting anything that hasn't been absorbed yet? If you crush up everything very finely and snort carefully it should be a non-issue. Again, your nose might get a little runny and in that case you should certainly wipe it.
4. Yes/no. You're unlikely to get a boost or anything 40 minutes later just because a little bit of active ingredient may have dripped into your stomach. However, whatever methylphenidate (versus binders/fillers) actually makes it to your stomach will be absorbed there as usual. Typically this is a negligible amount unless most of what's snorted ends up in your throat instead of your nose, but this is distinct from a drip.