League-of-legends – How to spectator mode be misused in League of Legends even with the 3 minute delay

You can customize the UI and use addons. One place you can look for addons is here, and this blog talks about an officially supported mod that allows you to change your UI, among other things.

I can't speak for Wukong specifically, but there are cases of "after cast delay". Or, if you're familiar with fighting game mechanics, it's essentially "recovery" time from executing the attack. Once the recovery period is up, then you're able to resume your assault - otherwise, you must wait.

There's two different forms of skill "recovery" that are implemented in League of Legends for some skills.

The one you're probably experiencing is simply that there is a short recovery period after the resolution of the skill where you cannot act. For example (and this may just be what you're experiencing), Nimbus Strike has a tiny delay between when you make contact with your staff and when you can start acting again. There's a short delay after Blitzcrank purges his Static Field before he can start moving, and Ezreal's Arcane Shift has a tiny delay after you arrive before you can use another skill or attack. The logic behind this is essentially an extension of the reason you can't use skills or attack in the middle of the action to begin with - you're still in the middle of using the other skill. It rate limits your ability to chain skills instantly together. Contrast something like Tristana's Rocket Jump, where you can use skills even in mid-air.

The other form is that some champions, namely Sona and Udyr, do have a forced cooldown on all of their skills after using any single one. In their case, this is to simply rate-limit their ability to cast their spells sequentially - no song spamming, and no ridiculous stance chains.