1. yes, most of the shopping malls and travel points are located near by the skytrain or MRT in Bangkok. Very easy to find and access..... The traffic jam is a serious problem in BKK, so taxi is not a good choice......
2. dont worry, some of the Thai can speak Cantonese, Mandrain especially in tourist shops, restaurants, night market...... Also, you can see many many HK ppls in BBK... just like the slogan of 7-11 shop "must have one HK ppl near by"
3. not prefer, limited hotel and airline to choose. For the airport transport or local tour, you can book it in advance before you leave. And the price should be cheaper than Hong Thai.....
4. Grand Diamond Suites Hotel -- old, not near skytrain..... not so good. For the 1st time, you are better to choose the hotel which is near the main shopping centre or skytrain, like Holiday Inn Bangkok, Aronma Hotel, Grand Hyatt Hotel, Continental Hotel.
1, You can check the price before you pay, normally the group ticket is cheaper.
2. How much is your budget??
Aronma Hotel only costs around HK$600 per night. It is old with the best location: Shopping Center - Central World Central is located opposite side, 5 mins walk to "Four Face Buddha" and skytrain station, Supermarket - Big C is just located in the next building. If you just need a bed for sleep and go out all the day. Aronma Hotel is a good choice.
If you want to pay over HK$1000 per night for the hotel, than you can choose Grand Hyatt, Four Season, Continental in the same region.
Holiday Inn Bangkok is located in the same region too, about HK$800 per night without daily breakfast. It's just renovated in 2004, overall is better than Aronma Hotel except the location. You can consider it too.
3. I never try the bus service in Thailand. For the Airport-Hotel transportation, I transit it by taxi without bring my kids or book a van in advance if I travel with them.
Taxi fare to Aronma Hotel: Around Baht450 (around HK$100) Hired a 7-ppl van: Around Baht1000 (around HK$200)
4. I visited to Thailand more than 5 times, but never visit to Grand Palace.
** FYI, there are some promotions for Holiday Inn Bangkok from CX holiday and Thai Airway before 30-Nov.