Baseball Starter Kit

That is a kids set so will be very small (unless you are a kid!)

You will need a bat (32" is the smallest adults use). Aluminimum bats are more expensive but they dont break and the ball travels further. Its easier to break a wooden bat than you think!

You will need balls (depending on where you play you could lose lots!)

You need gloves for each fielder (you could swap them each inning so you dont have to buy one each)

The catcher's gear will be the hardest to pick up & most expensive.
Its a dangerous position behind the batter and you get hit all the time. At the bare minimum you need a full face mask (and a cup!)

You need bases of some sort. You can buy flat rubber mats that work fine.

Batters should wear a helmet. The balls are hard.

Baseball Ireland runs a B league which is for people starting out. I'd reccomend getting in touch with your closest team and talking to them.
You should go to a few training sessions and pick up some tips. It can be a very frustrating game if you are doing the wrong things.

Where are you based?

Spartans play and train @ Corkagh Park, Clondalkin
Hurricanes play @ Corkagh Park but train in the Pheonix Park
Black Sox play & train @ Black Sox Park, Shankill
Mariners play @ Black Sox Park but train in Greystones

You can find all the contact info on baseballireland.com