What is the process and travel itinerary for applying for a 1 year multiple entry marriage visa in Savannakhet from Chiang Mai?

My journey from Chiang Mai to Savannakhet to apply for a 1 year multiple entry marriage visa (travel prices and times are approximate):

Flight from Chiang Mai > Khon Kaen:

(1000 baht, 1 hour)

Airport taxi to Khon Kaen bus station:

(180 baht)

Minivan to Mukdahan:

(300 baht, every hour. Journey time about 4 hours. There's a more comfortable bus, but only 1 a day and that leaves in the very early hours of the morning, so the minivan was the better option. It was an old van, but it had aircon and the seat was comfy enough. I've been on worse.)

Bus from Mukdahan to Savannakhet bus station:

(50 baht, every hour. You get on and off the bus 3 times as you go through immigration. The bus waits. It took 1 hour altogether).

My hotel was near the bus station in Savannakhet so I didn't need to use any tuk-tuks during the whole trip (Thai consulate was also in walking distance).

If you leave Chiang Mai on the 9am flight you can be in Savannakhet by 4:30 or 5:30pm.

Return journey was the same, except instead of the minivan I was able to get the much nicer Phet Prasert bus from Mukdahan to Khon Kaen. This left at 5:30pm and cost 250 baht. Arrived in Khon Kaen at 9pm.

If taking this same journey from Chiang Mai you'll need 2 nights in Savannakhet and 1 night in Khon Kaen on the journey back.

I went to the consulate on Monday, which is a busy day to go. I got there at 7am and was first in line and was done by 8:50am. If I had got there a bit later I would have been standing in line in the sun/rain for a few hours.

I brought all the recommended documents with me. My wife didn't come with me. The immigration officer asked "Where's your wife?" I said Chiang Mai and he said "Ok" and that was it. It looks like some other people had issues with this the following day so it'll be interesting to see what others report.

I didn't have a letter from my wife, but it might be a good idea to bring one just in case (maybe even bring the wife if you want to be extra sure, I don't know).

For collecting the visa the next day I got there at 12:30 and was near the front again. I got my passport earlier than expected, at about 1:30pm, with the 1 year visa stamped in my passport.

Thanks to everyone for the advice in this group before I went.