What are the options for household waste collection in Dublin city centre ?

Hi,

I'm looking to buy a house in Dublin city, probably near the city center. I'm seeing a lot of houses which have no rear access and on some streets you see wheelie-bins all over the place, some streets you see them in front gardens and on some streets you see none at all. So I'm wondering what are the options ?
(i) Is a homeowner required to be signed up with some waste-disposal company ?
(ii) Do you have to have wheelie bins or is it possible to use bags instead since space is scarce?
(iii) If using bins do you have to have 3 different ones (green, brown, black )?
(iv) how many sizes do the wheelie-bins come in (I've only noticed two, 'large' and 'skinny')
(v) how often are bins collected or does this depend on the provider ?

Thanks,

Usjes.