jackdd

Yes, every time you enter Thailand before the visa expires you will be allowed to stay 60 days, which can be extended by 30 days. So you can spend nearly 9 months in Thailand (making border hops in between) with a METV.

Which car / engine?

I've driven all over Thailand, stopped at check points more than a hundred times, they nearly always asked for a driving license. They might not seriously check it, but they ask to see it. Only the check points which you might encounter in the evening or night where they specifically check for drunk drivers don't ask for a driving license.

With the current prices you should always get E20, this is the cheapest fuel when looking at how much energy you get per baht. (because it contains more energy it lasts longer than E85, so less stops at the gas station required) If E20 is not available, then E85, if both is not available then 91/95

Every time you change your place you submit a TM30

No

This source is wrong, somebody with PR does not need to be reported http://library.siam-legal.com/thai-law/thai-immigration-act-temporary-stay-in-the-kingdom-sections-34-39/ Section 38 No, because a TM30 is not required for people with PR Yes

Afaik in general it's possible to do the TM30 by mail. So we should ask: Which immigration office does not accept a TM30 by mail? Anybody knows any?

The law/ministerial order regarding visa exempts does specifically say that you are entitled to get a visa exempt "many times". Why don't you use visa exempts if you leave every few weeks anway? Afraid that an IO is in a bad mood and will deny you for an arbitrary reason?

If you have some budget and want something special you might look arround "ban tawai", there are many shops selling furniture, and if you don't like what you see they also make furniture made to order.

If she has registered for the online TM30 before, then yes she can just do this.

Yes, this might be a problem But your GF could just file a TM30 before you apply for an extension (put the then current date or the day before on the form for when you arrived), then it won't be a problem.

The info on the UK embassy website is not correct 2 visa exempts per calendar year at land border crossings No written limit if you enter at airports, but if an IO is in a bad mood he might deny you because "you spent too much time in thailand"

No problem, people lose this all the time, he just has to fill out a new one at the airport before leaving the country

You will be the one paying the fines, the IO won't mind. This is published already, if you don't want to risk a fine just follow the written law. This means every time you stay or come back to stay somewhere where you are the owner, housemaster or possessor you have to file a TM30 for yourself. Afaik all changes to the application of the law which are done by the different immigration offices make following the law easier.