I would say 1-2 month before you complete your study/getting official result. It will take about 2 weeks in average to get an interview if your cv makes the cut and you pass the initial screening (phone interview, online assessment,etc). The selection process differs from one company to another so i advise you to spend some time research about the job scope and company that you want to apply for. Program like the management trainee/associate or any sort of graduate program from large company usually involves rigorous process with multiple stages so it could take up to more than a month to two.

Do take note of the job posting as well because some company will state if the job would require you to commence at certain month. You don't want to waste your time or theirs in interview if they're urgent in filling up a particular vacancy but you haven't made yourself available to work due to study.

if your results is excellent, you can try.
I prefer to have proven documents with me prior iv.

most of the friend i know under civil engineering ended up becoming IT programmer or other IT related job
reason?
environment issue
pollution issue
allergic issue
work life issue
time management issue
stress issue
money issue

if you have the passion and knowing your direction and what you wanna achieve....then go ahead and endures it
if you just go out there holding a paper and hope for the best...good luck, you might end up crying everyday looking for help to cope stress

If you like to work in the office then engineering is not the line for you.

No, you don't have power to command.

in any case they will have a box to fill in the application form.

Depends on company.. but personal experience says yes.

I have a colleague who applied for a job online, put 10k expected salary, the company never call. Update his profile there put 9k expected salary straight away got a call within a week.

Be ready to get scold. Ppl very rough in this field.

no, because they already have a number for fresh grad. they will just offer u. take it or leave it

If anything, I'd say low celery means you have low self confidence, hence a pushover at work, thus cannot deal with outsiders.

OR even worse, low celery = low skilled, meaning I have just fired another quota filling idiot.

Just put the "market norm" la.
Honestly, I've never landed a job where I lowball my celery. 

as per my experience with banking, even if you put 1000 as your expected, they will still offer what they have set for you.

but why put low salary just to score an interview?

usually all same. unless your role is very super niche. other than that, all fresh grad across dept will have same salary, standardized.

those who scored first class / master / phd may demand a little more than fresh grad

not much to begin with. like rm200-rm500

Don’t ask too many questions. Once you get into the real world you will know.

Sometimes we fresh graduates really cannot demand too much. We don’t have so many bullets to nego better just take what is on the table. Wait until 1-2 years when you have more experience on table and then you can demand.

Exactly like me, you sound like a desperate fresh graduate who wants to make the most out of your freshly acquired piece of paper awarded by the university because you passed all of their exams. You're are looking for somewhere to maximise learning experience, maximise earnings and maximise personal development.

The real world is like this, there is no absolute best choice that will give the most value. Soon you will realise there is no perfect fit. There will always be trade offs.

Many of the questions you asked have many different answers because different people go through different experiences. You can only learn what mistake not to make from there, what to avoid, what are the consequences of some options, but there is no absolute correct choice for you. For that you will have to find out about it by experiencing it yourself. It's called life.

u can apply 3 months earlier. when they hire new staff, they know they need serve notice period. u can tell them upfront as well only july u can start. they will probably ask if u can join earlier, see if u can do intern or drop by sometime

As long as you did not land any signature on any piece of paper stating your acceptance to the offered conditions, you are free to go. Black and white matters the most. Verbal acceptance and change of mind is about how well you negotiate your way out.