They will request your passport pages, delays your application a bit. Immediate cancelled applications are for biodata errors, rejections are for incomplete/unsubmitted documents after request.
The visa is valid for one year from the date of issue You need to re-enter before that 1-year date expires, effectively stretching it to 2 years. If you plan to travel in and out of Thailand after that expiry date then you must buy a reentry permit.
Free 60 day visa exempt entry stamp extendable another 30 days, available to more than 90 passports. These days more than 2 such entries back to back will raise eyebrows