Hi smegley - you've made the right choice with GPs rather than rabbits (but I've never kept rabbits so my view is skewed in a Guinea-Coloured Haze) 
Do you want:
indoor or indoor/outdoor (they can be kept outdoors all the time but it's difficult to monitor them. They don't cope with damp and draughts and extremes of temperature)
boys or girls- you can keep a pair of boys if they are 'bonded' or two + girls , or a neutered boar with 1+ sows.
adults or babies- adults, you'll know definately what sex they are. No surprise girl/girl that turn out to be boy/girl (been there)
There are loads of rescue hogs but you'd miss the cute piglet stage.
where to keep them- they need more space than the cages in the shops would lead you to believe, And they are quite vunerable WRT predators.
I keep my boars on cardboard (no staples or plastic/sellotape) topped with newspaper and hay. I put wood cat litter (rodent friendly) in their indoor cage for aroma control.
They don't smell if you keep them clean, it's mainly the hay.
Sawdust and shavings is generally not recommended as it's dry and dusty.It can irritate their breathing and dry their skin and fur.
Ours don't drink water, even though it's there. They have loads of veg.
My DD wanted boar pigs, so we got our two from a Rescue as 1 year olds. I have had mainly sows as a child. The boars are very affectionate characters, loving ,cuddly , food obsessed .
They are very close but when they are in their sleeping quarters they keep their distance unless it's cold.
Bear in mind your pigs will live up to 8 years (maybe more). You need to give them daily care .
Cleaning, feeding, checks. Cuddles.
A cavvy-savvy vet.- if they get ill, they do so quickly. Majority of GP illness is preventable.
Holiday care.
Lots to consider- but IMO (and my DDs) they are the BEST rodenty pets EVER 