hmm well i'm a plat 5-3 nami main, so maybe i'll have something useful - feel free to look at my build - i like to go frostqueen-tear-sightstone-mobi boots-upgrade frostqueen/trinket. then situational locket/zeke's if they have more ap/ad and then whatever your team needs.
my spell order is somewhat different from yours - i go qwwe and max wqe, in that order. i think q is more useful generally than w at lvl 1, especially if the enemy support has ignite and they hit 2 before you and all in, or if you get ganked at 2, or if you want to invade... you get the idea. then having 2 ranks of w at 3 is more useful than e imo, both for poke and heal.
as for gameplay, bubbles are just practice - practice max range, practice when they jump on your face or when you're running for your life, practice when they're tp-ing to a ward etc. everything else is pretty straightforward but if you have specific questions i can think about them.
your only real counter is blitz if you can't dodge grabs, but note that sona will outtrade you so don't even try, and recently i've noticed that bard does as well, but don't have enough experience vs him to say yet. also soraka is annoying and i hate her.
put a pink in the river bush asap. just do it.