With regards to cage size - the minimum size usually recommended in the UK is 360 square inches - about 2320 square cm. So, 60 x 40cm is the absolute minimum you should even look at. Note: this is footprint, and doesn't include shelf space. The Americans tend to recommend 450 square inches minimum. In Germany, by law, pet shops must inform hamster owners that the government recommendation is a minimum of 100cm x 50cm www.hamstercentral.com/community/705035-post7.html
Personally I find that hamsters do tend to appreciate having more space, and are much less likely to exhibit stress behaviours (e.g. bar chewing) when they have more space. There are also reports of hamsters that have shown aggression while in a smaller cage and have been perfectly tame once they've been moved to a larger cage where they're less stressed. While a cage the size of a coffee table sounds large, there are few homes that genuinely don't have the space to hold such a cage (our flat is tiny and we manage it....) and the hamster will always benefit more from a bit of extra space than you will...
If cost is an issue, then you can consider making a 'bin cage' - essentially a converted large storage box www.hamstercentral.com/community/diy-do-yourself-hamster-projects/36025-photo-guide-making-bin-cage.html
Hamsters do require more space than people tend to think - for reference, bear in mind that they have been recorded running up to 5 miles in a single night! They're active little creatures, and it's very sad that so many of them are neglected through ignorance and cages that are too small.
There's a good run-down of what a hamster needs from a specialist rescue here hamsterhavenhamsterrescue.weebly.com/hamster-care.html
With regards to species - Syrians are the largest hamsters, and are very common. They're what people often think of as standard hamsters. Ours is 150g and about 5" long. There are also some dwarf species readily available - mainly Roborovskis (small, very fast and difficult to handle but cute) and hybrid Russians (hybrid between winter whites and Campbells) (small, fast, and so prone to diabetes they need a totally sugar-free diet to reduce the chance of their pancreas packing up prematurely). I'd recommend a Syrian if you have children - they're certainly the easiest to handle. We've only ever had females, but some people do say that males are less active and easier to handle than the females.
Syrians are always solitary creatures. If you are looking at dwarves, same sex pairs can be kept, be aware that they do have some specialist housing requirements to avoid territorial fighting (no shelves, two of everything, no tubes, houses with multiple entrances etc. etc.) and can still need to be separated permanently if they start fighting. They also need specialist food - about the best food out there for Syrians is Harry Hamster, but dwarves need Burgess Dwarf Hamster mix (sugar free and easier for little mouths)