You may be very pleased to hear that in Thailand, unlike most other countries in the world, there are no death duties. You will be able to leave you all cash, stocks bonds and all real property owned in Thailand to your heirs without any deductions. In the case of real property (or any other property whose ownership is registered e.g a car) there will however be a transfer fee to pay (at a reduced rate) when the probate is final and the transfer of ownership registered.
There is no requirement to have a will in Thailand, however it is generally advisable to have one. If you die intestate in Thailand, probate will be slow, but eventually your assets would normally be deemed to pass to your spouse in their entirety, or if she had predeceased you to your surviving children in equal portions. Trying to effect probate locally, on the basis of a will drafted in another country is theoretically possible but can prove very slow and cumbersome.
Having said that Thai property can be passed on locally without any local Thai duties, you would also be wise to check the position in your current country of tax domicile, to see if they would be able to deem the Thai property a taxable part of your estate at home.
Import duties still apply to the importation of both new and used household goods and equipment - and these duties are still significant enough to discourage importation of all but the most specialist items or your treasured heirlooms.
Exceptions to the duty assessed on importation of household goods exist for three principal categories of person. Thai nationals returning to Thailand after having lived or worked aboard for one or more years, foreigners who are coming to Thailand holding a newly issued valid work permit and foreign retirees to Thailand holding a non-resident retiree O-A visa, may import a "reasonable quantity" of used household items. There is a catch here of course - since a work permit can take several months to issue after you arrive - but if your furniture arrives in port before the work permit is issued you can't clam tax free status - meaning you will probably have to stay in either a hotel or a semi furnished house in the interim.
A reasonable quantity, typically means a 20 foot container and not more than one of any type of household electrical appliance (T.V, Fridge, Microwave, CD Player etc.) Used typically means that it is not shipped in its original packaging.
All said, the one point every one I spoke to agreed upon regarding import of household goods, or particularly the electrical items was (that if you don't fall into one of the tax exempt categories) "Don't bring them". It will in almost all cases be cheaper to sell them where you are and buy new ones locally. By PhuketLand.