A lot of your timetable will be determined by the tailor shop: location, opening hours, etc. I might wait to exchange money in town as it can be advantageous especially in larger quantities, but understand you need some local currency upon landing. The three major mobile service providers: AIS/One-2-Call, DTAC/Happy, TrueMove (H), all have shops on level 2, Arrivals, near doors #5, 6 & 7:
http://www.suvarnabhumiairport.com/i..._mobile_en.php
I would avoid TrueMove (H) for now.
Note that any Friday, near the end of a month, and at the beginning of the month can be a bit crazier getting around, as people are settling accounts owing to salary day. Also the 8th of August is a national holiday so I imagine many people will take an extra long weekend.
I might start back to the airport closer to 13:30 as the SARL is experiencing some scheduling issues owing to a lack of working rolling stock, and you do not want to miss a Friday afternoon flight to Samui.