Tip 1: DOOOOOOOOOOOOOOOOOOOOOO ITTTTTTTTTTTTTTTTT-they are FAB!
Tip 2: Careful what you read! 
I didn't know about spikey willies and I kept GPs (admitedly mainly females and some baby/young male)
If you take the little boys, they will be going through their arsey stage at 6 months (Mine were a year old when I got them -missed all that
)
As much space as you can give them. There's a website that gives you a minimum cage size.
Mine have 5'5" X 5'5" outside (Playhouse) with a ramp and haybox.
Inside 4'X2'X 18". They don't think the indoor cage is good enough.We had a fight incidence last year (No blood but nasty) so the indoor cage is seperated into 2 .
They've got a big rabbit run for summer (IIRC 7'X4') but not used it yet.
Make sure they always have hay, pellets and water.( GP pellets have Vit C, so don't give them rabbit ones)
There's lots of food threads what they can/can't have (some things are toxic for GPs)
Megazorb is a horsebedding- it's made of wood pulp (I bought from Farmway online). Don't give them sawdust or shavings-it's an irritant.
You'll find what works for you .Fleece(nice but you have to really shake the bits off before you wash them) Hay-to sleep in and eat. Shredded paper.
We give ours dog bowls, big enough to share without squabbles and don't get tipped up.
They are usually healthy if their diet is right, just be aware of cold and damp.They can have respiratory problems and don't lke extremes of hot/cold.
Boys have agrease-spot that needs a wash. Nails need cut. Check for bites/mites/abcesses (especially if they argue). Check their teeth, but eating keeps them trim.
Impaction is usually older boys ( Am I looking forward to that
) vom face.
They are lovely little ceatures. This is our first pair of adult boys, and are very spoiled. We got them from a local rescue, only 10 minutes.
Your journey will be fine if you get a big carrier (or 2 if they travel seperate) put in a towel for accidents and hay to keep them busy.Add some cucumber to quench their thirst