Good questions and good thinking.
You don't say how you are going to "do" the G, by liveaboard or land based, but largely the answer is the same.
Be prepared for:
1) Small boat back rolls upon countdown command
2) Immediate descent bordering on negative entry
3) Lateral (sideways) current and how to play it, ducking behind boulders, etc
4) Possible hand-over-hand crawling (it's all lava rock, but did you bring heavy gloves/)
5) Vertical Currents (Downwellings/upwellings)
6) Shooting your safety sausage from 25' and hanging on a line at 15fsw, wait for pick up
7) Taking gear off and handing up to DM
8) Going up less than ideal ladder
9) Seasickness (if a liveaboard)
10) The potential of spending quite some protracted period adrift. This is unlikely, and many ops have added beacons, but this does not obviate the need for this exercise and learning experience. Previsualize spending 12 hours in the drink. What would you do, and when would you do it.
You want reassurances? There are none.
You want real world advice? Go to Speyside in Tobago.
My SO decided she wanted to go to Galloping Pogos. OK, fine, follow me.
She first logged 100 or so in the calm waters around Roatan in the most ideal of conditions and boats.
Then we went off to Tobago so she could get a taste of Galapagos Lite. She logged 35 dives there on several small boats in way less than ideal physical infrastructure. Rickety wooden ladders, small boat recovery, doffing her gear and passing it up, negative entries, shooting her marker from depth and practicing surface survival techniques. These included alternative signalling methods, dropping weights, dropping tank, maintaining body temp and more. Forewarned is forearmed.
In Tobago, she learned lateral currents. She also learned to ask the DM questions and pay attention to the answers.
In Tobago she handled a pretty stiff downcurrent quite well several times and got more proficient throughout the week. She did such dives as Heart Attack, Japaneese Gardens and African Express. Then she stepped up to Washing Machine and aced it.
On her first downcurrent dive in the G, she was apparently enraptured with the Hammerheads below us at Gordon's Rocks. Luckily, a DM from Scuba Iguana grabbed her as she descended through 100fsw. Hate to train a new one.
So, go and train. If you want realistic conditions, try Tobago first. It's no guarantee of success, but with your logical quest for preparedness, it will assist in your path.