Night scene in Rayong is quiet on weekdays, weekends it's got its own buzz. 2 malls in the city, both with theaters. Lots of restaurants in the malls and on the beach. One discotheque that I know of... Could be more. And a small expat community...
The company bus is very rarely owned directly by the company and most are running under contract to the company. There is no contract or payment required from you. Just be at the stop on time. ☺️
Yeah, Rayong city is in the centre of multiple industrial zones. When we were living there, my fiancée was picked up and dropped off by the company bus. There are song-taews out there but the routes are limited and the frequency is low. Given the traffic that you saw I'd recommend a personal 4 wheeler rather than 2 for safety's sake.
I would also suggest that you speak with the company regarding pick-up and drop by their 'contract bus' if they have one. 90% of the large companies have this.
You most definitely need your own transport for Rayong and the surrounding areas. Song-taews shut down by 8pm. Minivans are available till around 10 and motorcycle taxis are not recommended in the late night.