You can also get the buses to those tourist spots in the east from Morchit bus teminal but as Ekamai is located just next to the BTS station, getting the bus here may be more comfortable.
You can distinguish 2nd class buses by their orange stripe on the bus body.
Also, keep in mind that when you get to the station you might be asked for your destination and call to take these kind of buses- the orange stripe one. Avoid them, though, it's cheaper but remember it gonna take longer time,too.
So, buy the ticket from the ticket windows and ask for 1st class bus or "Rod Por Nueng" (in Thai).
The weak point is they have only 3 buses a day (6.30, 7.45, 9.45)
So booking in advance is unnecessary unless you plan to travel on long weekend or public holidays.
It's the bus from Roong Reuang Coach company which is only provider for Pattaya route and have bus leaving for Pattaya from every bus terminals in Bangkok.
Waiting area inside the terminal.
Food stall is in front of the terminal with English menu.
Inside the café
Drinks cost between 40 - 55 baht.
Even you're full, visiting here may be neccesary as going to beaches without sun lotion is disaster.
To go to Khao Sarn area you can take bus no.2 to Ratchadamnern Ave.
Anyway, the traffic on Sukhumvit road is always jammed. You'd better use BTS for your first hop and then change to taxi or bus somewhere else.
For example, to go to Khao Sarn road, take BTS to National Stadium station and wait for bus no.47 at the bus stop in front of the stadium for Ratchadamnern Ave.
BTS station is just next to the terminal, walk out and turn right at the street then you will see the entrance.