Hi Hon,
Bangkok airport is enormous and very busy. The staff are very polite and helpful. Most people arriving are OS tourists and the Thai's are courteous to a fault.
Declare the money, they are totally use to OS people carrying cash etc. Your laptop is personal property and probably doesn't need declaring. I didn't declare mine. Queues can be long just be patient and follow the instructions, Signs are in English and Thai so there are no issues there.
The average Thai earns very little, so a Baht100 tip is massive and very well appreciated. If you travel by taxi the driver will ask for the toll road fee so don't be surprised if a driver asks for money on the trip to pay the toll.
As ever be polite and if you are in doubt about something ask. Most Thais in public roles speak English. It is a safe city to visit, unless there is a terrorist alert, then just follow the official guide lines.
Politics in Thailand is volatile so keep out of discussions. The King is sacred so NEVER say anything about the Royal Family. Corruption in public life is rife but will not affect you.
If you are going for GCS a car from the clinic will probably collect you. I went to a conference and arrived at 2 am, I took a taxi to my hotel and was quite nervous, but there was no issues at all.
I have to admit that the Thai people are some of the most courteous, accepting and welcoming people I have met in any country.