Pros

+Nami's team fighting is good if you can land the ult and Q the carries.
+Nami's kiting is good with her Eed autos slowing.
+When in lane your W will make it easy to trade poking with then hitting you then you healing it right after.

Cons

-Nami doesn't have a strong escape sure she has a speed up from her passive but if she gets ganked she will get in a tough situation.
-If you take her top(A place where I love to take her) she is not too tanky so you need to make sure you have a tanky jungler.

These are good spells for top but personally I prefer the normal ignite flash just to make sure I get the kill and I don't mess up on my Q which will make the difference in a 1v1

With your AP quints you can get the boost of AP at the start of the game.

Your marks will help when top against the tanks, or if you go mid it will be good against those weird tank Elise jungles.

The cool down glyphs will help with the longer cool downs.

The armor seals will help against the ADs top lane(you can switch these out for magic resist if you're mid)

Nami is a great top and mid laner, she has good poke and has a strong importance in team fights with her ult and Q. In a team fight her W is good since she can bounce between enemies and heal your allies. When you take her mid you need to make sure you don't get poked out but with your heal you can nullify that.