I'd choose Vientiane or Vietnam. Marriage visas irrelevant. Provide your home address only if asked, or required for a Thai address. Money can be in a bank anywhere.
If staying at a hotel initially, enquire and be sure they file a tm30, actually it should be done whenever you stay at a new place, but, if you aren't going to need services for 90 days at immigration then as you say you can forget about it. That said, you'll need to make sure a TM30 is filed in the immigration jurisdiction before you file a 90 day report. You'll also need another TM30 filed upon returning to Thailand even if you stay at the same address as well as doing your 90 day report in person 90 days after you return, you can enquire at the local immigration office about their policy on this reporting after returning from abroad, but most will require it. In theory you'll only be filing one 90 day report on each entry, possibly two depending on whether you bounce or get an extension (not recommended). So in all likelihood each 90 day report will be done in person.
At this time, the Thai tax laws only provide for earned funds transferred into Thailand being liable for tax. Those funds would then be subject to the dual taxation agreement if one is in place.
Leaving and re-entering requires no new registration. You have your multiple entry visa and fulfilled the application requirements. You only need to produce the printout of the approval PDF or show the sticker in your passport.
what part of he got his visa yesterday and also believes he needs a sticker to prove primary DTV, leads you to not deduce that he got an e-visa and he ain't gonna get a sticker?
My reply was that he doesn't need the sticker, just a copy of the primary DTV holder approval to apply for the dependant DTV. Then you chime in to say some places give stickers and some don't. Well yeah. He will never get a sticker, though his dependant might depending on where they apply.
What you have or don't have and how you got it is irrelevant. There's no mention of e-visa in his post because he is likely old school and unaware of electronic filing and e-visa approvals, he thinks he needs to pickup the sticker somewhere because of his approval email, which he doesn't realize is the actual visa he needs to print out. You basically stated the obvious to me, why I dunno.
by law you are supposed to have a TM30 filed within 24 hrs of staying somewhere. So your friends landlord should add you to their TM30 filing for their address. Failing that just do what I suggested above. The TM30 should be filed in the jurisdiction where you'll be requesting immigration services such as extension or filing TM47 (90 day report).
PS... on the grand scale of things it's no big deal, but you'll need to file a tm30 to do the 90 day report wherever you are at that time.