Once you have applied for an extension of stay, the multi-entry visa is actually void. So dont leave with the intention of returning without a reentry stamp. Once you get the extension, you can add either a multi or single reentry stamp at imigration. The multi allows you to freely exit and return as many times as you like, and stay as long as you like within the year, there is no 90 day limit. (Its not quite a year if you go for another extension towards the end of the 2nd year, as again the reentry stamp becomes void at point of applying for next extension).
officially you dont need an IDP or translation as your license is already in English. However some local DLT's do seem to insist on the IDP as its easier to work with and is an international standard
understand what your saying. But i believe the starting point is that you would owe tax on the 65k you bring in for the last 10 years, and you would have to prove with supporting documentation for those 10 years that you have already payed tax in your home country and there is a DTA in place so reducing or negating the tax obligation.
except its better to fill one in, as technically anyone who has stayed over 180 days is subject to a tax audit, and with a tax return this is limited to a 5 year period, where as its 10 years without one. (Not a new rule). Not that i've seen anyone mention being audited. But you also need 3 consecutive returns if you ever want to go down the permanent residence route. But yes 99% of retirees will never have looked into their tax obligations.
you tell the government via the yearly tax return of all remitted monies, and you supply details of home country tax payments to reduce/negate any payments to Thailand tax office. This has always been the case, just that from now on you cant get tax credit for untaxed income earnt out of country post
officially yes, but officially you have to wear a helmet on a motorbike. So if your a tax resident you are supposed to apply for a TIN at local tax office after your first remitence after you have reached 180 days, and then file a tax return by the following March 29th. This has always been the case and hasnt changed. However 99% of expats never bother, and from what i have read, most tax offices have histoically said don't bother as the DTA's and old loophole usually meant there was no Thai tax to pay, and its just extra work for them with no gain. I can't see this changing, but if you do do a tax return and detail your remitance, you have to include a copy of your uk tax return or P60 i believe to prove tax paid.