Question 1: Does side effects occur due to basic or minimum of Buddhism Precepts or Sila (requirement) not been achieved yet?
Yes. Right speech, right action, and right lively hood are all foundational virtues. If your morality is not in check, the mind tends to be busy. The side effects that occur due to the above precepts not being adequately followed include but are not limited to gilt, anger, fear, worry, frustration, and the cultivation of complicated and trouble causing situations.
The reason why they suggest tackling the above before meditation, is so that you can stay focused. It is easy to be distracted if you try to meditate when, due to poor morality, you have cultivated pervasive mind states.
You could still meditate before getting your life into a peaceful state, but you make more work for yourself if you don’t.
Question 2: As a lay Buddhist, is it a right practice if the sequence is wrong or Sila/Precepts and Meditation being practiced together? If no, then at what stage of requirements? Well, i know at least not after being drunk and go meditate.
As a lay Buddhist, the order doesn’t really matter. The order only matters if your goal is to become enlightened. Each layer makes the next one easier to achieve. By having good morals it becomes easier to meditate. By meditating you train the mind to be more able to observe the universe as it is and gain wisdom.
If you are meditating for some other reason than to train the mind to cultivate wisdom, such as to de-stress or energize the body, just make sure you set the right environment to achieve what you are looking for. If your goal in meditation is to enhance concentration, don’t drink beforehand. If your goal is feel peaceful, don’t murder someone the day before.
Just know if you don’t follow the suggested order, the next link in the chain will be harder to achieve.