katekebo wrote:
1) Are these islands accessible by a 17.5 ft roundabout, or will I be
stretching my luck trying to go there in my boat?

Depends on how seaworthy your particular boat is. Not all 17.5' boats
are the same. Having said that, I've seen people at the islands in
craft I wouldn't take outside the harbor. Summer time squalls come up
in a hurry so be careful. You can be easily caught with a storm
between you and the mainland.
If you're feeling lucky, I recommend staying in the Gulfport/Ship
Island channel. At least that way, if you get in trouble, there's
usually some traffic coming and going.

2) Which are the recommended spots to anchor and swim?

Anywhere on Ship Island is fine. If the wind/surf is up, anchor on the
north side and walk across. Anchoring on an end is a good idea, so you
can scoot around to the leeward side if necessary. You can also tie up
to the dock at the Fort on the north side and walk across the
boardwalk to the swimming area on the south. There's a snack bar,
restrooms, showers etc over there.

Which are the places to avoid?

Anyplace on East or West Ship is fine in a shallow draft boat such as
yours. Watch for shallow on the north side.
On West Ship, the east end of the south side is generally accepted as
a nude beach if that's of interest one way or the other.

Cat island has always been privately owned but portions of its current
status is a bit in question. The Gulf Islands National Seashore was
supposed to buy part of it but rumor has it they've backed out. You
might check with their headquarters in Ocean Springs about that
(Google for phone # etc) . Even so, most of Cat is still privatly
owned. People tresspass on it all the time but I wouldn't advise
anyone to do so out of simple respect for the owner's rights. Fishing
its waters is perfectly legal though.

3) Any specific restriction, dangers, or precautions are should take
into account?

Common sense rules. i.e. jet skis have been banned at Ship Island due
to idiots drowning themselves trying to make the trip. There are also
a miriad of other Govt rules. No camping on the island, things like
that. Weather should be your first concern in a small boat. The chop
can become extremly steep in the sound and it happens very quickly.

4) Can you recommend me any good boat launches in Gulfport

Gulfport Harbor has an excellent boat launch and parking facility. No
charge.

5) Besides these two islands, can you recommend me any other beaches or
swiming spots, preferably closer to the Rigolets?

How about a nice river? There are plenty of them, with sandbars etc.
Take your pick. That might be a better idea in a small boat.

Have a nice trip,

Rick