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.