Guinea pigs are social animals and need to be in pairs or groups, so yup yup get 2 of any gender that can't breed (male/male, female/female or neutered male/female/s). If possible first look into shelters and rescues around you to adopt some existing piggies rather than buying from a pet shop or breeder. It'll likely be the same price or cheaper than buying from a shop and you're saving some poor unwanted piggies.
That cage is fine if a bit small for 2 pigs but you can buy the grids and coroplast and make an identical or bigger one for less. Lonin made hers for £45(/$68 without coroplast, but things are expensive here :B We just use a shower curtain underneath) and it's equivalent of 2x5 with a lid. They're really easy to make just slot them together. Not all guinea pigs will use ramps and upper levels don't count in floor space so that cage is 9sq ft when the ideal minimum for 2 pigs is 10.5. Especially if you get males they do better with a bit more room so if possible go for 10.5sq ft (2x4 in grids or bigger) of lower level floor space and possibly skip the upstairs.
Cats and dogs shouldn't be a massive problem as long as you have a lid and preferably have the cage in a room the animals can't or don't always access. C&C cages are very sturdy, especially if you use cable ties. Lonin has a cat and her (very shy and timid) guinea pig isn't bothered by it (others died, we're getting more in a few weeks). We had to add netting to the grids since she could stick her whole paw in up to the shoulder, though. XD Depends on your animals. Guinea pigs aren't the most interesting of things to most cats.
They also need regular floor time outside of their cage to run around and explore a bigger area. They need a good quality pellet food made for guinea pigs, avoid muesli if possible and definitely anything with seeds or coloured bits. They need unlimited fresh timothy hay and a daily variety of vegetables and occasional fruit (
piggy safe fruit and veg). Avoid hay racks, just stick it in a corner or in a box/tray. They can get stuck in hay racks and break legs.
For bedding you can use something like carefresh or megazorb or you could look into fleece. Layer it with towels underneath then you don't need to buy bedding. Remove any visible waste daily and then just brush it off outside every 5-7 days and wash it.
Give them lots of houses, tunnels, cardboard boxes. Anything they can sit in, on, run through or eat they'll enjoy.
They're prey animals and so can be quite skittish. They'll probably run away from you to start with and depending on their personality they might always. If you get a brave one it'll stand up on the bars begging for food/attention/cuddles whenever you go by. Nearly all will be happy to chill on your knee(or chest, or shoulder, or hair), they just don't always like the process of being picked up. c:
You need to have money saved up for vet bills since guinea pigs have weak immune systems and are prone to URIs. Any changes in behaviour or weight loss and you need to take them straight to a vet. They hide illness so by the time they look physically ill it might be too late to save them. Lonin had one we spent over £100 treating him then he needed to be put to sleep the next week anyway. :c And that cost another £40.
If you haven't already read through
http://www.guineapigcages.com/ http://www.guinealynx.info/ and
http://www.cavyspirit.com/ especially the social life section for safe dominance behaviours. Piggies can seem to be doing some scary things to each other which are actually harmless. Especially as they hit 5-12 months and start becoming grumpy teenagers they might have a few squabbles. XP Basically as long as they aren't drawing blood it's safe to keep them in the same cage because they'll likely work things out. c:
Think around 80~ dollars, probably. Look up C&C cages and they are the exact same thing. ^^;
Hope that helps!
