You will have to talk to an insurance agent to get definite answer about coverage of pre existing conditions.  Insurances are crooks and I for one don't think they will cover it.  Don't  have any idea about your other two questions. 

Another option you could research on is MA healthcare.  I believe State of Massachusetts has free health care even for foreigners.  Couple of my friends treated their parents for free in MA.  It wasn't cancer but something like arthritis, chronic back pain and general checkups.  I think the hospital only needs a proof of residency.  It could be easily obtained by opening a bank account with MA address.  May be try calling one of the hospitals.