There is no easy answer as it all depends on your case , but having meaningful status in at least 2 alliances is always better, so keep your AC status also if possible

Study your flight patterns and see what will work for you , its possible that adding UX might also work for you or not

Google flights and the FB XP chart will become your friends for the next months

Prices are not regulated and they can quickly change , the covid and pre-covid fares are a good reminder , so take that into account

As others said , test a bit to at least get to FB silver and then see how things goes , if you like it or not

I would recommend to really work on your strategy during your "silver year" , study the details of flying blue, skyteam , the FB partners , the DL/AF/KL/WS/VS joint venture , etc..... go beyond the marketing of airlines and "bloggers" advertisers

You have a lot to learn , for instance some pros of being a free agent you mentionned are easily manageable as FB member ,and as FB and skyteam member , your flights wont be limited to just AF/KL/DL , you just need to know the game so open your mind and see further than what you know

But if you have any questions you are at perfect place to ask them