Yes, you get visa at the consulate not the embassy

Tha Li border several km north of the town, have been a few times by motorbike, pretty "middle of nowhere" place :-)

Go to immigration on Monday

Good decision, sit on the 400k at least until you have the year extension.

^Latest major policy change was 31-Dec-2016 visa-exempt entry now limited to 2x per calendar year by LAND, but by air no stated limit, and it's 30 days by air or land (before most just got 15 by land). But yes you can now do consecutive visa-exempt entries. Back to back tourist visas also no stated limit of consecutive times, at the discretion of your friendly consular visa boss.

Allow around 60-90 minutes for simple border hop. There is 8am bus arriving 1230 then one coming back at 1400, or take the next one to allow more relaxed pace.

Green Bus to/from Mae Sai one way

V-Class 319 Baht

X-Class 205 Baht

A-Class 160 Baht

Fly back in no problem, 30 days visa-exempt. Maybe try Thai consulate in Vientiane next time for SETV, more user-friendly.

Can be done 15 days before or 7 days after the stated report date.

From where to where? In most cases easy and cheaper to do it yourself.