1-year visa and a re-entry permit. Not an issue with immigration.

Do a quick flight to KUL or SIN and return on the next flight.

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Royal Jordanian does an evening flight BKK-KUL-BKK ... (RJ 180 / 181)

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Easy enough to fly down, go to the transit desk to get your boarding pass and catch the same plane back to BKK. You never enter Malaysia so no need of wasted space in your passport.

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Just go down on a flight, go through the transit gate and return on the next flight. Then do your Thai visa when you return (been there, done that, got the T-shirt).

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The only space used is your exit stamp from Thailand and the 30-day entry stamp on your return.

Do a quick flight to KUL or SIN.

You don't even need to enter the 2nd country.

Just go down on a flight, go through the transit gate and return on the next flight.

Then do your Thai visa.

In house legal advisor / consultant is possible within a Thai law firm or consulting expert in a MNC. You cannot practice the profession of lawyer within Thailand.

A work permit is possible.

2000-5000

If you depart before the 7-days-over is up then no need for the 90-day report. Passport control at the airport won't be a bother. They just stamp you as gone.

When you return your 90-day clock starts again.

If you take 8 days then you need to do the report or face a fine.

If flying in/out then no issue. If you can afford to fly every month then they are happy that you are spending money here. (There no restriction on entries if you fly).

Land crossings however currently have a 2/year limit for no-visa entry.

He should based on marriage be able to get a non-O the same as your guardian visa. You will need an authenticated marriage certificate (probably already have for your own visa).

IF he gets the O-visa then he will also need to get a multi-reentry permit.

Proof of funds is not usually needed at the border for a non-O. Even at that, having a valid credit card in your wallet takes care of that issue.

Immigration (passport control) here won't care.

You may need an exit flight if you are coming in on a visa exempted entry. The check-in counter when you board your flight is where that comes up. They may refuse to board you or they may require you to sign a waiver protecting them from liability if you are denied entry.