You will arrive in Indonesia in Terminal 3 and only need to switch to the domestic side of Terminal 3 after you clear immigration, get your bags, and clear customs. There are plentiful free luggage carts to move about. I am not super versed on arriving in Jakarta and transferring since I live here, but I think there is a decent chance you won't be able to check in to your Garuda flight for a few hours and unable to access the lounges as they are past security. Assuming you are coming from the US, you might consider getting a day room at the airport hotel or Capsul hotel. If you are anything like me, you will be beat up and exhausted. A shower and a couple of hours in a bed will be worth its weight in gold...or at least it would be for me. I think you can get six hours and a shower in the capsul hotel for something like $30.
The lounges will have comfortable waiting room seats, some Indonesian food and snacks: noodles or fried rice, soup, maybe some cold small sandwiches, sweets, etc... I am pretty sure no beer, booze, or showers. Comfortable and clean but underwhelming.