At Suvarnabhumi Airport, it's located just before passport control at International Departure Gate 2. You need to check in, clear security screening, and then you can get the re-entry permit counter.
Go here.
International Departure Gate 2 is the easiest to find that counter.
, not all immigration offices accept extension applications 45 days in advance. Most offices allow you to apply for an extension within the last 30 days.
, not all immigration office accepts that emailed PDF records. Those offices only accept the one from a bank branch. Check with your local immigration office in advance if emailed PDF is acceptable there.
So you applied for Non-ED visa inside Thailand and it was approved on 25 March.
The first 90 day count starts with the first extension application usually.
You will need to apply for the first extension at the end of the current 90 days (means around the middle of June). Check your due date on that time you apply for an extension with your local office.
And please remove the unrelated photo from the post. It makes things confusing.
, you don't need to provide lease agreement in that case, but you may provide the proof of relationship (marriage cert, etc) to show staying in that address is legit.