I can only offer second hand experiences.
I have a friend, also a LHP, who has played in Japan, Korea, Mexico, South American leagues.
He enjoyed Japan the most. Said the organization were pro, facilities nice and you are treated well (good food, travel, medical). It probably helped he was making serious money in Japan.
He enjoyed Korea as well although everything was a slight step down from Japan.
Mexico he played in off and on for about six years. There are a lot of American players (guys like your friend, A-AAA guys and older ex MLBs) so it can be a little easier adjusting. There are several Mexican leagues of differing qualities. He said the league he played in last (Pacific?) was about equal to AA or AAA ball. Decent facilities. The team he sued for put the foreign players up in an apartment complex with ages guards am thy would take a van to the games....with two M16 yielding guards.
Overall he enjoyed his experience but said it can be a dangerous place and you need to keep your wits about you. You had your choice of payment, direct deposit, check or cash. Yes, the GM would come in once a month with literally a bag of cash to pay the guys who wanted to be paid in cash.
A bit of the Wild West. He said he never ran into issues getting paid correctly in Mexico or Japan or Korea. South America he had some issues.
Also said there are two pay scales, at least the last league he was in in Mexico. One for Mexican players and one for foreign players.
The season is shorter and leagues run at different times so it is possible to play close I year round. He was getting paid about $60,000 American for a 5 month or so season.
He said the biggest challenge at first can be loneliness. If you end up on a team with no other English speakers it can be rough.
Also, like baseball everywhere it is cut throat. Your training, recovery injury treatment is often left up to you (outside of Japan).
As a 37 year old he was offered an invite by the Yankees and turned it down to play in Mexico. Why? No taxes and you can do whatever you want as long as you are ready to play. So he could fly home for 5 days to see his kids and fly back for his start.
A lot of things to consider. For
What he said it is a mixed bag. Not going to get wealthy playing foreign ball and it is not an easy go but you are making your living playing ball.