1. Nope, just a handwave is all it takes to summon it. Besides it's standard equipment, he starts with the dagger already in his hands.
2. Yes he moves through the shadows, yes that's true. It's not like Kai can follow him or predic where he would come up. And as i said he can just take his hand out and stabby stabby. I never said it's instant, but it might as well be as Kai cannot do anything in the mean time, except to wait to be stabbed by a hand from a place he doesn't know.
3. Even then nagi can just shadow bind him inside the shadow world to keep him from escaping.
4. Not really. And yeah "speed is equal here" whereas Ikki was faster yet he stll couldn't get the first move. And that is arguable at best. Him having 500 years of experience doesn't mean much without feats. Him having 500 years of kung fu experience means nothing against a guy who has mastered 128 sword fighting styles by the age of 15, is a master at using all types of weapons including spears and other kinds, is stupidly good at hand to hand combat being able to bring out 100% of his power channeling his energy to effortlessly stop even stronger people, disarm, dodge, hit, etc, can copy any swordfighting style with a mere glance, can fight and copy while unconscious, can perfectly abuse the living bodies, knows all about the force and vectors, can reflect attacks, can disperse energy by blocking, knows the strength of an opponent from a single glance, knows if the opponent is talented or hard working with a sword clash, is an expert marksman, can predict hits, can understand the biology of someone, stay in the opponent's blind spots 100% of the time, and iirc can even use the pressure points like oogway does. Etc. Kai's age doesn't give him an edge just cus "age ftw" when it comes to skill departament Rakudai is pretty stupid, i don't think anything from Kung Fu Panda can even compare. Yet that still didn't give him a "i hit first cus lol" because he still has to close the distance and stuff, while Nagi can just wave to do his stuff.
5. Go try that actually. Go out in the sun, turn 180 degrees and tell me if your shadow moves in any significant way. And i've explained why he can still catch him off guard by just taking part of his body out to stab. There is no way Kai can hit him first if he's literally coming out from where he needs to stab, he needs to move like what, 2 cm at best.