From Chiang Mai to Puhket area

Just take trains and buses or mini vans and stop along the way. Get a guide book or go to Sukothai, Lopburi, south of bangkok check out Hua Hin, Prachuab, Ban Krut, etc. etc.

If time is critical just get a couple of cheap flights. Google Nokair.com or Airasia.com. For Feb 2015 there is a CNX to DMK fare every day at THB736 and departing every hour or so, then 5 flights a day to HKT. Here is a link to the sample fares
AirAsia has 3 direct flights a day

After Bkk, head to Chiang Mai and do the north for 4-5 days. Take buses back to Bkk, stopping off at Ayutthaya and maybe Sukhothai, then fly from Bkk to the south.

Hi

I've been to Thailand before and i'm actually doing something similar again in January 2015.
I'm going to get a flght with Air Asia from Chiang Rai to Krabi. If you dojnt have much time i would fly. The prices are cheap if you book in advance.

You could take a Nakon Air VIP coach (approx 10 hours) from the Bangkok's coach terminal ( when you land go to information and ask them directions to coach terminal), or Nok air from DMK airport fly into Chiang Mai. Its faster than the trains (13 hours).

Thanks for all the replies and recommendations. I know that flights are cheap and a lot faster, but we wanted to experience at least once traveling by train there. What do you guys think about my new plan?

-First 4 days in Bangkok.
-Than heading north, by train and/or bus planning 5 days to get to Chiang Mai, stopping at Ayutthaya, Lopburi (seeing some monkeys) and maybe also Sukothai and Lampang.
-Than 4 days in Chiang Mai (hiking, visiting the caves north from Chiang Mai).
-Afterwards, taking a flight from Chiang Mai to.... now this is the question... we want to visit both Andaman Sea (Phuket and/or other islands nearby) and the Gulf of Thailand (Ko Pha Ngan). Maybe first fly to Phuket than traveling to Ko Pha Ngan, make a stop at Khao Sok National Park.
-At the end probably fly back to Bangkok taking our flight back home.

According to this plan we would have 12 days in the south. Is it realistic to do all this in just 12 days? what about the rest of my itinerary? Thanks in advance for every reply

It is realistic but there is travel time to consider but the journey is often equal to the destination.

Yep, I reckon you have nailed it there given your overall time allowance and trying to maximise what you can fit in that time. Daisy chaining Ayutthaya, Suk, Lopburi etc makes no sense at all by air, but land transport works. Avoiding backtracking saves a lot of time so the CNX - HKT flight makes a lot of sense and saves a lot of time and is pretty cheap. Have a great time.

Madanapelle2: I would have agreed with you prior to doing PNH to REP by road..... and numerous other uncomfortable time-consuming disasters with sod all - or endless repetition - to see.