1 - A 2x4 C&C cage is the ideal size for a pair, the 2x4 is the number of grids used and each grid is usually 14 inches (if I remember correctly, I use closet shelving instead of grids).
2 - Some do like cuddling, some don't. It depends on the individual. Most all guinea pigs will quickly realise you are the source of food and will love interacting with you for the chance at food, but they will never like being picked.
3 - I think it is generally accepted that guinea pigs are crepuscular, but pet guinea pigs will sleep and be active whenever suits them day or night. They don't have a set "sleep" period (likely due to the need to have food constantly moving through their systems), they take naps when they feel like it. Some guinea pigs have even been known to do exercise by doing laps around the cage at unusual hours (like 3am).
5 - Yes they poop a lot. Most will poop during lap time, you will occasionally have an individual who will hold it. The poop should be hard and not smelly unless there is something wrong. Do keep in mind they do two kinds of poops, cecal and fecal, they re-eat the semi-digested cecal poops (usually they bend over and grab it from their bottoms as they do them) these poops are often green and apparently have an odour to them (I've never gotten to see one, they are very protective of their cecal poops) the fecal will be what you find in the cage these are brown with very little odour.
6 - Yes, guinea pigs are herd animals. A friend of the same sex is necessary unless one of them is de-sexed. They will need to be introduced properly, see this link for info about that
https://guinea-pigs.livejournal.com/3002707.html
7 - This is personal preference, the most favoured type of beddings on this forum are fleece and uhaul pads or fleece with wood pellets. To use fleece you first need to prepare it so that liquids will wick away rather then pooling on the surface, to do this you need to strip the fleece of its coating (often by lots of washing with hot water, detergent with no fabric softener and bleach - don't worry it won't lose its colour). When using fleece the most important factor is what you put underneath to absorb the urine, which is where the uhaul and wood pellets come in, and you need to remove the poop daily or twice daily. Wood pellets seem to be the most favourable option, the only downside being their weight, as you do not need to change them for weeks with proper maintenance and there is almost no odour (make sure the pellets do not have a strong scent or it can cause repository damage to the guinea pigs).
8 - Not usually, sometimes you will get a traumatized guinea pig that will bite. If your guinea pig bites you when you pick it up you should look into the possibility it could have mites which make it painful when touched.
Also please adopt, don't buy from a pet store. There are many homeless guinea pigs in shelters and pet store guinea pigs are usually sick, pregnant, inbreed and they often come from breeding farms that keep them in horrible conditions. It is the general stance of this forum to be pro-adoption and anti-breeding (the anti-breeding is due to the dangerous nature of breeding guinea pigs, as the babies are very large in relation to the sow at the time of birth the risk for complication is high, couple that with the fact they can get pregnant again within hours after they birth and the baby boys can impregnate mum from 3.5-4 weeks of age).
It is also generally frowned upon to purchase directly from a breeder due to the shear numbers of guinea pigs in shelter or being re-homed on craigslist, these breeders add to the over population issues (not to mention certain types of guinea pigs, such as satins or roans, are prone to severe genetic defects, such as osteodystrophy and lethal white syndrome, that it is very irresponsible to breed them).
