I am looking into installing a wireless networks in a residential
complexes to enable landlords to provide high speed connection to
tenants. This could be also the case for a hotel providing connection
to guest. My question is:

1-  What are the regulation on DSL or cable modem bandwidth (bandwidth
reselling)? Is it only based on the user agreement of the ISP? Any
legal or financial liabilities.
2-  A list of ISP?s in California that doesn?t care about bandwidth
sharing. (earthlink, is one, SBC is definitely against it, no wonder)
3- What are the different plans and prices existing today that serves
this purpose.  (I think it?s referred to as provider rate plan  ...)

Depending on the size of the residential complex/hotel, a Cable or DSL
line might not do the trick and you would need to lease a T1.

Not realy, you can get 4 port load ballancing rounter that can combine
up to 4 lines of DSL. But if you are looking into symetric there is no
question that T's are the answer.