A few things I've found out....Martinique

It seems a lot of the same questions have been posted but not many replies.
So, as I'm here... I'll say what I've found out. Yes, you can arrive the same day to express d isles and buy your ticket to move between islands. They have a buy 3 trips get 1 free at the moment. If you have your ticket, They want you to be there 1 hour before the boat leaves, and they board(they say)30 mins before departure. So if u want to buy your ticket same day... Get there at least 2hours early but of course the sooner the better...you can always buy them , leave and come bk later.
They don't travel between the islands everyday so check out their site first for the days and times. (yes, they don't seem to answer their phones, but I sent an email, and DiD get a response and Could buy my tickets with credit card ahead of time. )
FDF near the port didn't seem like a very nice place to stay...maybe 1 night if necessary, but it seemed better to go esewhere.

I went to trois ilets. 60euro taxi from the airport.(about 30mins) Or if you get I time to take the Last ferry (20min ride and 4.euros one way or 6.50 RT) at 18:45. It seems the boat leave every hours at :45....meaning starting at6:45 until 18:45 every hour.unless bad weather, then they will not go and you are stuck with the taxi.
No ferry the Sunday...all day nothing.
For a reasonable hotel that clean, has a pool and super central La Pagerie..for about (60e )
Or bigger budgets... Bakoua 160euros (infinity pool, pretty view)and up. Or Carayou . And of course nicer and right on the beach(not private...so you can stay at the Pagerie and just come us the "nicer"beach.)

It seems the best way to move about is renting a car. Otherwise Collectives, group vans, that move about (1.40 a distance) but it seesms not are completely direct and you have to change at least once...waiting for the next passing one to come by....but you are on vacation right and have a bit of extra time. Otherwise taxi , again, but pricey.

Trois ilets they says is a big touristy place but doesn't seem that way to me. Several pizza and crepe ride places, 1boulangerie,1grocery store...but not much to do besides beach or boat day trips they offer you. no real seafood either. Weird. (one walking distance "Village Creole" about a 15 min walk out of the center area... I was told it was good local food (finally!) it just seems to me like a cute area but not extremely" touristy"as the guides say. If you want to hang on a beach for a few days...like 3-4, ok, but otherwise you'd really want a car to go see other areas. I imagine Martinique has much more to offer than just here.

So, best advice...rent a car and move about. It seems that way you can stop and stay where you want. Seems rooms are always about.
Voila.
Happy travels