Here's a picture of several small craft presumably training as a swarm.
Next, we see a nasty little craft, the Zolfaghar class, that carries two small Nasr-1 anti-ship missiles in cannisters and two torpedoes in the small bulges on either side of the cabin.
Here's a picture of a boat with what might be a ZU-23-2, twin cannon 23 mm gun.
Here is a boat firing a 107 mm rocket from a launcher atop the cabin and mounting a machine gun on the bow. The rocket reportedly has a range of around 5 miles although in unguided mode against a relatively small target like a warship (compared to trying to hit somewhere in a city), the effective range is presumably much less.
Next we see an RPG being fired from a small boat.
For a bit more variety, small craft can also be used to lay mines.
Here's a Seraj class boat. Note the rocket launcher atop the cabin.
Here's a nicely armed boat with rocket launcher, bow cannon, and stern machine gun.
Here's the same boat type shown launching a rocket from the launcher atop the cabin.
Here's a British made, very fast Bladerunner reportedly being reverse engineered for swarm attacks.
And, lastly, here's a Ya Mahdi high speed, unmanned boat. Iran claims that it's radar evading due to its high speed. I'm not sure they understand how radar works.
That gives you a feel for the variety of swarm craft and their weapons. This is not meant to be comprehensive and I'm quite likely wrong about some of the identifications. Feel free to jump in and correct me.
Bear in mind that these are the smaller swarm craft. Iran, and other countries, also operate somewhat larger missile boats that would attack from much longer distances. As one might expect, there is some overlap between the two broad categories of boats. Of course, the problem with missile boats is that the missiles generally outrange the boat's sensors, requiring the boat to approach much closer than strictly necessary.
Still, the variety of boats and weapons coupled with the purported numbers has to give a naval force pause for thought especially in the confined waters of the Gulf.