Thailand forum

I can only make suggestions re the Thailand bit.
And there it depends a lot on budget - can you afford to fly between Bangkok and Phuket ? (do a search - lotsa cut price flights) - if so the best route would probably be Bangkok to Phuket airport - ferry to Phi Phi - ferry to Krabi /Railay - Phang Nga Bay (either from Krabi/Railai to the south Bay or from Phang Nga town for the north and central bay) - bus to near Phuket airport.
If you can only afford a bus (may not be all that much cheaper than a budget flight but an overnight bus will save a night's accommodation which is a big plus for low budget travellers) - then it would be overnight bus to Phang Nga town for Phang Nga bay trip - bus to Krabi - ferry to Phi Phi - ferry to Phuket - bus to Bangkok.

Notice both options have you going thru Krabi/Railay - great area if you can afford a night or two.

Three weeks in total right? You may need to set some priorities re. Chiang Mai (Songkran), Laos, and the southern beaches, especially if you're not prepared to do a couple regional flights. A logical circuit could be Chiang Mai for Songkran, then north Laos for a week and back via Bangkok to the south but maybe not enough time for all those beaches you listed. Or do Laos first (Bangkok-Vientiane, VV, LP) then pop into north Thailand and fly Chiang Mai to Phuket (Air Asia, cheap if you book online well in advance) which would give you more beach time. Without any flights you're looking at some long (all-day or all-night) bus or train rides, effectively spending most of your trip in a seat struggling to connect the dots.

Thanks for the ideas, I know three weeks isn't much time. So far this is what I've revised my timeline to be like for now.

Arrive BKK, spend a night or two
Overnight train to Chiang Mia (Songkran, although its throughout Thailand, people say this is THE place to be)
One week slowboat/bus through Laos LP-VV-Vientiane
Back to BKK for another night or two
Fly to Phuket (I can't believe how cheap it is)
Phi Phi
Phang Nga Bay
Fly back to BKK

My next question is if there is something I should not miss out on doing while at any of those places. Obviously you can't do it all and not everyone likes the same things but it's nice to have all the options laid out.

Thanks for the responses so far, travelfish has an amazing community.

A lot of people go to Phi Phi and stay in loud, crowded Ton Sai with its two not so good (in most parts) beaches and never see the nicer areas of the island.
I personally think the east coast beaches are some of the most laid back in Thailand. Long Beach on the far east of the south coast is a very good compromise - nice beach, pretty relaxed but with some life and not too isolated as far as trips into town to party and shop. A big turn-off in all areas of Phi Phi is that it tends to be more expensive than most islands for accommodation. Darn place is popular just about any time of year.

Alternatives in the region include the Railay area of Krabi, Ko Lanta and Ko Jum. The last is the most laid back although the southern beaches on Lanta rival it; Railay is the most scenic but budget accommodation is a bit scarce (April being shoulder season should be more reasonable) - Ton Sai the climbers' beach next door has lots of good budget accommodation and a nice vibe; and Lanta has the most variety although it is a bit more off the beaten track for a time-short traveller.