If you're at the level you sound like you're at, don't waste your time with multishines. You'll get a lot more millage off of shine grabs or a retreating aerial after your shine hits shield. The occasional double shine is useful though. Too many fox players think the first thing they should learn is multishines when in reality it's not a very useful strategy. Unless you're perfect (not going to happen) they'll either grab you when you mess up, you multishine their shield then jump away and it resets to neutral, or they buffer roll out. Practically it's not very good. When you have options like retreating aerials to combat their grab attempts and shine grabs which lead into other combos like uair, it's much better.
But yeah to answer your question c sticking aerials is pretty optimal most of the time because you have full control over your character as you can use the analog stick to move while doing your aerial whereas doing it with A would require you to move a little bit in the direction of the aerial. Also fast falling a dair would require a second down input after the aerial (pretty much not gonna happen) or for you to press down for your dair after the peak of your jump which you don't always want.
Waveshine -> usmash (only works on characters that don't fall down from shine and don't move too far away from shine) waveshine->jab reset -> anything (only works on those who fall down from shine and don't move too far away from shine) waveshine->grab waveshine->nair waveshine->dair and waveshine->waveshine are all excellent followups, especially the first 3.
