You need to narrow down your choices -- see collegeboard. Then contact the universities you are interested in once you've sorted out the SAT, ACT, etc. Some universities prefer one over the other.
Some want the writing section of the ACT and some don't. In any case, many private universities will have a writing requirement to fulfill as part of the application process.
Financial aid -- FAFSA site here. But contact the universities you are interested in to find out what exactly they require. Many private universities require the CSS Profile which is on the collegeboard site in another section from the one above. You will need tax returns handy as well as other info such as salary, estimated value of house(s) and other property, stocks, shares, trusts, etc., when you fill out your forms.
Most good universities will be able to help you get all the paperwork sorted out, both wrt academic requirements and financial aid, and the visa process too.
If you contact universities by phone, it might be a good idea to buy minutes from some place like celtictel.com. Much cheaper than standard international rates.