They need a huge amount of space, including things that you might not think about...larger litter trays, carriers, bowls...doorways
lol
I've found that the food amount needs to be dramatically increased...although I know that many members won't agree with me on this point. (I've just never been able to keep a giant's condition on a small amount of pellets/greens and tons of hay. River has a large bowl of pellets a day and greens that always include carrot/apple, as I've found she needs that extra calorie boost. She is such a good hay eater and has golden poops....just needs the extra. In the winter she gets the odd tablespoon of porridge to help.
Companion size isn't so important, but temperament is. Frenchie's are very very relaxed buns who will very easily get annoyed with a tiny bouncing Nethie, but Conti's are generally more tolerant of the smaller, bouncier breeds. All I will say is that if there WAS a fight between a Giant and a Nethie it's pretty obvious who would come off worse.
Handling...it depends. I've never had a bun who won't let me pick them up....I've had a couple who enjoyed it. Then we got River. The power of her back legs means it's utterly impossible to pick her up, even for a moment. We're very well versed in carrier moving, and she's learned to just hop in it if we need to move her. I check her underside by making her periscope. Giants have VERY delicate backs, so you don't want them to struggle in your arms and fall funny.....I'm sure a few will remember what state Eddie was in when I got him.
Any other questions I can try to answer. I love big buns!!