First two weeks of Nov - Phi Phi and Koh Lanta

Hi

We are travelling first two weeks of November to Thailand for the first time.

We haven't booked anything except for flights and overnight train down to Krabi.

We were planning to split our time between visiting Phi Phi Island and Koh Lanta.

Does this sound like a good plan for the time we have and time of year?

Yeah November is the best time to go. Especially early before high season rates take effect at some resorts. You can fly air asia into/out of Krabi and then there are ferries that connect Krabi, Koh Lanta and Phi Phi. Maybe go to Lanta first since its the most "remote" of your destinations. Its also the quietest of the three areas. Good day trips to emerald cave and such from Lanta, then you should try to do a day or two in Railey Beach just because its a cool area, before going to busy busy Phi Phi.

Yep, your plan sounds fine to me.
I kinda like supra's suggestion of a day or two at Railay (or adjacent Ton Sai) - the normal downside of this area, overcrowding, will not be a factor early November.
I'd also mention a stopover for a short time on Ko Jum between Krabi and Lanta if you can squeeze it in.
Got a page each with lots of information, pix on all these locations here -
http://tezzasthaiinfo.blogspot.com/2007/06/index.html

Note you can't catch a train to Krabi - there are no lines remotely close. Either fly or bus.
If you are a train freak you can catch a sleeper train into Trang, go across the road from the station to one of the small travel agents and get a miniubus right onto Lanta via the vehicle punts.

You can get more and often cheaper flights into Phuket and catch a ferry to Phi Phi - about the same distance and cost as Krabi Phi Phi. No trains to Phuket either. Lots of buses.

Plan sounds good, Railay in Krabi is well worth a visit - arguably one of the best beaches in Thailand. You can take long tail day trips out to Bamboo island, chicken island etc which are great for seclusion for the day. Koh Lanta is very slow and much less touristy than the rest of the Pha Nga province, very locally based tourism which is great for cheap, wholesome thai food cooked by fantastic locals. Phi Phi in my opinion is well past it, very commercial and the building never seems to stop - don't get me started on the daytrippers - its like a cruise liner arriving in the caribbean for the day! Still a beautiful set of islands if you can avoid the overly commercial side though. Have fun!

I'd save the best (Koh Lanta) til last, as it's much more relaxing than Phi Phi. If I had a choice between the two, I'd go for Lanta. To me, Phi Phi is too crowded and expensive. Lanta is pretty quiet in November, but the weather is lovely and you will have fun.