Not sure if it's OK to ask 2 questions, but here goes:

1. I just managed to get a double entry tourist visa. I would appreciate it if someone could confirm or put me straight about my understanding.

I have 2 months, which should take me up to mid March. To claim the next 2 months(to mid May) do I go to an immigration office or do a border run. At the end of that period (mid May), I should be able to pay for a month's extension, at the behest of the immigration office of course. After that I should be able to then start doing the 3 sets of monthly border runs.

2. A friend is on his first OA visa and would qualify as married or retired. Last year he got a confirmation letter from the British Consulate in Chiang Mai regarding his financial status. The visa is coming up for renewal and he's wondering if he has to get another new letter from the consulate for the forthcoming year or will he be able to use the one from last year.

Many thanks, in anticipation.

1. I just managed to get a double entry tourist visa. I would appreciate it if someone could confirm or put me straight about my understanding.

I have 2 months, which should take me up to mid March. To claim the next 2 months(to mid May) do I go to an immigration office or do a border run.

You have to cross any international border, then come back to use the second entry.

You can think of it as having two visas. Note they indeed cost double of a single visa.

At the end of that period (mid May), I should be able to pay for a month's extension, at the behest of the immigration office of course.

Yes, the one month extension is straightforward and can be done at any immigration office in Thailand. Bring 1800 baht and passport pictures and a copy of the passport pages with your picture and the passport page with your visa (and entry) stamp.

After that I should be able to then start doing the 3 sets of monthly border runs.

You can do as many border runs as you like as long as you don't stay over 90 days in any 180 day period. So that could indeed be three entries of 30 days each on visa-exempt stamps.

A friend is on his first OA visa and would qualify as married or retired. Last year he got a confirmation letter from the British Consulate in Chiang Mai regarding his financial status. The visa is coming up for renewal and he's wondering if he has to get another new letter from the consulate for the forthcoming year or will he be able to use the one from last year.

Best to go to the nearest immigration office and talk things over. My guess is that the document would need to be current. (But that's a guess)

Sorry, could actually be 1900 for an extension.. or 1700.. Heck, bring 2000 baht and have some money left over for some ice cream.

I'm not sure if you could extend your first entry that way, actually. Possibly someone else on this forum has tried that.

I have 2 months, which should take me up to mid March. To claim the next 2 months(to mid May) do I go to an immigration office or do a border run. At the end of that period (mid May), I should be able to pay for a month's extension, at the behest of the immigration office of course. After that I should be able to then start doing the 3 sets of monthly border runs.

You do realise you can extend your double tourist visa twice? First extension can be done in mid march when the first 2 months/visa runs out. So that takes you to mid June. Then you cross the border, come back in and get your second lot of two months. When that runs out you can extend again for a month. So your visa is actually good for a 6 months stay.

Extension cost is 1900 for 30 days.