You really don't want to all in till 6 unless you have Jungler's help. You don't yet have enough damage because you only have 2 damaging abilities till you get ult and all of your cooldowns are really high. Focus on trying to out farm your opponent. Typically you will face an ap mage who will have a hard time farming without using abilities which is nice considering you have such a high starting AD because you are considered a melee attacker but just have a bit more range. No one expects your all in damage because you are considered a support.

Pros:

+People don't expect high damage burst from a support
+Great Roam potential
+Great team fight
+The more ap you have the tankier you are(Passive shield and Q heal scaling)

Cons:

-What cons?
-Only cons I see are in raKAN
-For real tho not much.
-Clearing super minions can be very diffucult (as that is usually the mids job)
-AD mid laners are hard for you most of the time.

Legit it's harder to play full ap rakan mid in normals. In ranked people think you are trolling and play super cocky which you can punish them for. In normals people just play... well, normally.