Learn English – Ourselves or Us

Number 1, with "as of", is correct. The "as of" is optional: you could just say, "He issued the certificate effective April 2014."

If a document or status has no particular end date, we usually say that it is effective "as of" the start date. If it does have an end date, then we say "from" and "to" or "from" and "through". Like, "The certificate is effective from April 2014 to March 2015." But it's not necessarily wrong to shuffle the words round. "... effective as of April 2014 through March 2015" would be unusual but not jarring.

We don't normally say "being effective" in this context unless it's in a subordinate clause. Like you might say, "The certificate, being effective as of April 2014, is not relevant to the incident under discussion, as that took place in March 2014."

You could say "being effective" if describing a state of having impact. Like, "You know you are being effective when you start to make enemies." You'd rarely use such a sentence to describe the "start date" of a document, but maybe with some effort you could come up with a plausible example. Hmm, like, "There used to be a 30 day delay between issuance of the certificate and the effective date, but now they are being effective the day they are issued." Awkward, I doubt anyone would really say it that way, but maybe something of that sort.

The "subject" that ourselves references is implied in the sentence.

We could write the idea this way

It's also a time for us to relax our mind and discover ourselves when we stroll around unplanned and without any specific purpose.

We can sometimes leave out parts of a sentence that are "needed", because our listener can infer or understand that those parts are "there".

The rules that describe when and how we can do this are complex. The relevant grammar topics include "linguistic ellipsis" and "substitution".

As I was reminded in the Language Overflow chatroom, these pronouns are not always used reflexively. Consider She did it herself. Notice that she didn't do anything to herself. Some linguists call these emphatic pronouns.